Computers, Sensors, MILs, CELs, PCM Inputs and More

[ExplorerDMB]

COMPUTERS ​

The use of computers on automobiles has expanded to include control and operation of several functions including fuel delivery, ignition systems, emission systems, climate control, lighting circuits, cruise control, anti-lock braking, electronic suspension systems, and electronic shift transmissions. Some of these functions are the responsiblity of the power train control module (PCM), while others are functions of what is known as a body computer module (BCM). Most recent vehciles have computers/modules for just about everthing (a seperate computer for the engine, seperate one for the transmission, sepereate one for the ABS, and so on).

A computer processes the physical conditions that represent information (data). The operation of the compute is divided into four basic functions:

1. Input - a voltage signal sent from an input device. This device can be a sensor or a switch activated by the driver or technician.

2. Processing - The computer uses the input information and compares it to programmed instructions. The logic circuits process the input signals into output demands.

3. Storage - Program instructions are stored in an electronic memory. Some of the input signals are also stored for later processing. A "keep-alive memory" voltage is always constant to the computer to keep the memory intact.

4. Output - After the computer has processed the sensor input and check its programmed instructions, it will put out control commands to various output devices. These output devices may be the instrument panel display or a system actuator. The output of one computer can also be used as an input to another computer/module.



Analog and Digital


The computer is capable of reading only voltage signals. The program used by the computer is "burned" itno ignition control (IC) chips using a series of numbers (binary numbers 0's and 1's). An analog voltage signal is continuously variable within a defined range. For example, engine coolant temperature sensosr do not change abruptly. The temperature varies in steps from low to high. The same is true for other inputs such as engine speed, vechile speed, fuel flow, and etc.

Compared to analog voltage, digital voltage patterns are square shaped because the transition from one voltage level to another is very abrupt. The simplest form/generator of a digital signal is a switch.

An Analog Signal

An Digital Signal

A Common Binary Code Chart



ROM, RAM, PROM = Memory


Read Only Memory (ROM): Contains a fixed pattern of 1s and 0s that represent permanent stored information. This information is used to instruct the computer on what to do in response to input data. The CPU reads the information contained in ROM, but it cannont write to it or change it. ROM is permanent memory. ROM contains the basic operating parameters for the vehicle.

Random Access Memory (RAM): Constructed from flip-flop circuits formed into the chip. The RAM will store temporary information that can be read from or written to by the CPU. RAM stores information that is waiting to be acted upon, and it stores output signals that are waiting to be sent to an output device. RAM can be designed as volatile or nonvolatile. Volatile RAM, the dta will be retained as long as current flows through the memory.

Keep Alive Memory (KAM): KAM is a version of RAM, but is connected directly to the battery through circuit protection devices (fuses, etc.). The Microprocessor can delete KAM information, but once the ignition key is turned off, the KAM retains information. KAM will be lost when the battery is disconnected, if the battery drains to low, or if the circuit opens (blown fuse). Nonvolatile RAM will retain its information if current is removed.

Programmable Read Only Memory (PROM): Contains specific data that pertains to the exact vehicle in which the computer is installed. The information may be used to inform the CPU of the accessories that are equipped on the vehicle (4wd, a/t, a/c, etc.). The information in PROM is used to define or adjust the operating perimeters held in the ROM. PROM
can be removed and replaced with an updated PROM.

A PROM Chip

Erasable PROM (EPROM): similar to PROM except that its contents can be erased to allow new date to be installed.

Electrically Erasable PROM (EE-PROM): Allows changing the information electronically one bit at a time. The flash EEPROM is an IC Chip inside the computer. It is possible to erase and reprogram the EEPROM without removing this chip from the computer. Seen in most cars today. Here is an example: Reprogramming


Hope this is somewhat informational for some people. Anyone else want to put in a few words, please do. To read information on how to TALK to the computers, check out this thread: Scanners . Also, to see what codes computers send out, go to here: OBD II DTCs


Glacier991 has written a thread on Oxygen Sensors. This thread is a wonderful thread with a lot of great information. I suggest everyone read it before replacing a single O2 sensor. http://www.explorerforum.com/forums/showthread.php?t=149917

-Drew

 

[Glacier991]

I plan a new series here. I stopped before because there was no interest. Damn the lack if interest. I am going to do sensors, tools and hopefully the use of an NGS.... realizing no one will have one but so they know what their dealership CAN and SHOULD do. Between transmissions, I hope to encourage knowledgeable folks to post here...... like you. Sparky, and others. Who knows I loan everything else including a trans tester these days (My tools are full loaned at the moment which makes me feel good).. maybe someday I can loan a NGS tester.

 

[dogfriend]

For people who want to learn about Electronic Engine Control, but don't know where to start, I would recommend getting a copy of this book:

http://www.amazon.com/gp/reader/0837603013/ref=sib_dp_pt/002-1298272-7522403#reader-link

It covers EEC-IV but a lot of it applies to EEC V as well. Unfortunately the author died, so it won't get updated, but it is a really good explanation of the Ford EEC-IV system. It explains how the PCM, sensors and actuators work together to control the fuel injection system.

 

[MONMIX]

yeah scan tools make life SO much easier.

I look forward to your writting Glaicer, I know you know your stuff.

 

[Glacier991]

Dogfriend is right (as usual). Probst's book IS the EEC-IV Bible.

If you want to really get inside the EEC-IV, a bunch of computer geeks reverse engineered it.... their stuff is a little esoteric and definitely electronic geeky, but fascinating.

Here's a link to the home page of one of these interesting fellows. Dogfriend, notice what he shows on his website as "the bible" !

http://www.kvitek.com/ford/

The 80 page pdf will bowl you over.

 

[dogfriend]

Now you did it - now I am actually going to have to find time to read all of that stuff


Seriously, I like learning about this stuff from an engineering point of view. Ford EEC-IV and EEC-V are basically automated control systems designed to meet multiple requirements - power, fuel economy, emissions, etc. They are actually reasonably easy to work on if you know how the system is supposed to work and what the various components are supposed to do.

I have seen Glacier get frustrated (and I have also shared this) when you read a thread where someone got a Check Engine light so they replaced the O2 sensors and it didn't fix the problem. Now they want to know what to replace next. They don't even know what codes are causing the CEL.

The components are too expensive to take a "shotgun" approach at fixing the problem. I am an advocate of testing the components whenever possible to verify or eliminate them as the cause of the problem. Otherwise you will just waste money.

 

[Glacier991]

Yeah I am thinking when somoene posts a thread entitled somethig along the lines of "Help, MY CEL light is on - Do I need new Oxygen Sensors?" they should be FORCED to come to this forum and read everything before they are ever allowed to post again.

OK, that was harsh.

Just take em out back with a rubber hose.

 

[sparky2263]

MIL (Malfunction indicator lamp)

The Malfunction Indicator Lamp (MIL) alerts the driver that the Powertrain Control Module (PCM) has detected an On Board Diagnostic (OBD) II emission-related component or system fault. When this occurs, an OBD II Diagnostic Trouble Code (DTC) will be set.


The MIL is located on the instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or ISO standard engine symbol.
Power is supplied to the MIL whenever the ignition switch is in the RUN or START position.
The MIL will remain on in the RUN/START mode as a bulb check during the instrument cluster proveout for approximately 4 seconds .
If the MIL remains on after the bulb check:
The PCM illuminates the MIL for an emission related concern and a DTC will be present.
The instrument cluster will illuminate the MIL if the PCM does not send a control message to the instrument cluster.
The PCM is operating in the Hardware Limited Operation Strategy (HLOS) .
The MIL circuit is shorted to ground.
If the MIL remains off (during the bulb check):
Bulb is damaged.
MIL circuit is open.
To turn off the MIL after a repair, a reset command from the Scan Tool must be sent, or three consecutive drive cycles must be completed without a fault.
For any MIL concern Symptom Charts. See: Computers and Control Systems\Testing and Inspection\Procedures\Diagnosis By Symptom (Includes No Start Test)
If the MIL blinks at a steady rate, a severe misfire condition could possibly exist.
If the MIL blinks erratically, an intermittent open B+ to the bulb or an intermittent short to ground in the MIL circuit exist. Also, the PCM can reset while cranking if battery voltage is low.

 

[sparky2263]

Catalyst Efficiency Monitor

The Federal Test Procedure Catalyst Monitor monitors the catalyst system for deterioration and illuminates the Malfunction Indicator Lamp (MIL) when tailpipe emissions exceed the appropriate Hydrocarbons (HC) emission thresholds. It is called the FTP catalyst monitor because it must complete during a standard emission test (the Federal Test Procedure). This monitor relies on the front and rear Heated Oxygen Sensors (HO2S) to infer catalyst efficiency based upon oxygen storage capacity. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the rear HO2S quite slow compared with the frequency of the front HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines, and the rear HO2S begins to switch more rapidly, approaching the frequency of the front sensor. In general, as catalyst efficiency decreases, the switch ratio increases from a switch ratio of 0 for a low mileage catalyst to a switch ratio of 0.8 or 0.9 for a low-efficiency catalyst.

Many Low Emission California vehicles will monitor substantially less than the entire catalyst volume in order to meet the stringent catalyst monitoring malfunction thresholds. In many cases, only the front, light-off catalyst is monitored.

Front and rear HO2S switches are counted under specified closed loop fuel conditions. After the required number of front switches are obtained, a rear-to-front HO2S switch ratio is calculated. The switch ratio is compared against a threshold value. If the switch ratio is greater than the emission threshold, the catalyst has failed. Inputs from the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) (warmed up engine), Intake Air Temperature (IAT) (not at extreme ambient temperatures), MAF (greater than minimum engine load), VSS (within vehicle speed window) and TP (at part throttle) are required to enable the Catalyst Efficiency Monitor.
The DTCs associated with this test are DTC P0420 (Bank 1) and P0430 (Bank 2). Because an Exponentially Weighted Moving Average is used for malfunction determination, up to six driving cycles may be required to illuminate the MIL.

 

[sparky2263]

Comprehensive Component Monitor

The Comprehensive Component Monitor (CCM) monitors for malfunctions in any powertrain electronic component or circuit that provides input or output signals to the PCM that can affect emissions and is not monitored by another OBD II monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or proper range of values. Where feasible, inputs are also checked for rationality, outputs are also checked for proper functionality.

CCM covers many components and circuits and tests them in various ways depending on the hardware, function, and type of signal. For example, analog inputs such as Throttle Position or Engine Coolant Temperature are typically checked for opens, shorts and out-of-range values. This type of monitoring is performed continuously. Some digital inputs like Vehicle Speed or Crankshaft Position rely on rationality checks - checking to see if the input value makes sense at the current engine operating conditions. These types of tests may require monitoring several components and can only be performed under appropriate test conditions.

Outputs such as the Idle Air Control solenoid are checked for opens and shorts by monitoring a feedback circuit or "smart driver" associated with the output. Other outputs, such as relays, require additional feedback circuits to monitor the secondary side of the relay. Some outputs are also monitored for proper function by observing the reaction of the control system to a given change in the output command. An Idle Air Control solenoid can be functionally tested by monitoring idle rpm relative to the target idle rpm. Some tests can only be performed under appropriate test conditions; for example, transmission shift solenoids can only be tested when the PCM commands a shift.

The following is an example of some of the input and output components monitored by the CCM. The components monitor may belong to the engine, ignition, transmissions, air conditioning, or any other PCM supported subsystem.

Inputs: Mass Air Flow (MAF) sensor, Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor, Camshaft Position (CMP) sensor, Air Conditioning Pressure Sensor (ACPS) , Fuel Tank Pressure (FTP) sensor.

Outputs: Fuel Pump (FP) , wide open throttle A/C cutout (WAC) , Idle Air Control (IAC) , Shift Solenoid (SS) , Torque Converter Clutch (TCC) solenoid, Intake Manifold Runner Control (IMRC) , EVAP canister purge valve, Canister Vent (CV) solenoid.

CCM is enabled after the engine starts and is running. A Diagnostic Trouble Code (DTC) is stored in keep Alive Memory and the MIL is illuminated after two driving cycles when a malfunction is detected. Many of the CCM tests are also performed during on demand self-test.

 

[sparky2263]

EGR System Monitor - Differential Pressure Feedback EGR

The Differential Pressure Feedback Exhaust Gas Recirculation (EGR) System Monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the Engine Coolant Temperature (ECT) , Cylinder Head Temperature (CHT) , Intake Air Temperature (IAT) , Throttle Position (TP) and Crankshaft Position (CKP) sensors is required to activate the EGR System Monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test.

The differential pressure feedback EGR sensor and circuit are continuously tested for opens and shorts. The monitor looks for the Differential Pressure Feedback EGR circuit voltage to exceed the maximum or minimum allowable limits. The DTCs associated with this test are DTCs P1400 and P1401.

The EGR vacuum regulator solenoid is continuously tested for opens and shorts. The monitor looks for an EGR Vacuum Regulator circuit voltage that is inconsistent with the EGR Vacuum Regulator circuit commanded output state.

The Diagnostic Trouble Code (DTC) associated with this test is DTC P1409.
The test for a stuck open EGR valve or EGR flow at idle is continuously performed whenever at idle (TP sensor indicating closed throttle). The monitor compares the Differential Pressure Feedback EGR circuit voltage at idle to the Differential Pressure Feedback EGR circuit voltage stored during key on engine off to determine if EGR flow is present at idle. The DTC associated with this test is DTC P0402.

The differential pressure feedback EGR sensor upstream hose is tested once per drive cycle for disconnect and plugging. The test is performed with EGR valve closed and during a period of acceleration. The Powertrain Control Module (PCM) will momentarily command the EGR valve closed. The monitor looks for the differential pressure feedback EGR sensor voltage to be inconsistent for a no flow voltage. A voltage increase or decrease during acceleration while the EGR valve is closed may indicate a fault with the signal hose during this test. The DTC associated with this test is DTC P1405.

The EGR flow rate test is performed during a steady state when engine speed and load are moderate and EGR vacuum regulator duty cycle is high. The monitor compares the actual Differential Pressure Feedback EGR circuit voltage to a desired EGR flow voltage for that state to determine if EGR flow rate is acceptable or insufficient. This is a system test and may trigger a DTC for any fault causing the EGR system to fail. The DTC associated with this test is DTC P0401. DTC P1408 is similar to P0401 but performed during KOER Self-Test conditions.

The MIL is activated after one of the above tests fails on two consecutive drive cycles.

 

[sparky2263]

Evaporative Emission (EVAP) Leak Check Monitor

The Evaporative Emission (EVAP) Leak Check Monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or greater than 1.016 mm (0.040 inch) in the Enhanced EVAP system. The proper function of the individual components of the Enhanced EVAP system as well as its ability to flow fuel vapor to the engine is also examined. The EVAP Leak Check Monitor relies on the individual components of the Enhanced EVAP system to apply vacuum to the fuel tank and then seal the entire Enhanced EVAP system from atmosphere. The fuel tank pressure is then monitored to determine the total vacuum lost (bleed-up) for a calibrated period of time.

Inputs from the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor, Intake Air Temperature (IAT) sensor, Mass Air Flow (MAF) sensor, vehicle speed, Fuel Level Input (FLI) and Fuel Tank Pressure (FTP) sensor are required to enable the EVAP Leak Check Monitor.

NOTE: During the EVAP Leak Check Monitor Repair Verification Drive Cycle a PCM reset will bypass the minimum soak time required to complete the monitor. The EVAP Leak Check Monitor will not run if the key is turned off after a PCM reset. The EVAP Leak Check Monitor will not run if a MAF sensor failure is indicated. The EVAP Leak Check Monitor will not initiate until the Heated Oxygen Sensor (HO2S) Monitor has completed.

The EVAP Leak Check Monitor is executed by the individual components of the Enhanced EVAP system as follows:


The function of the EVAP canister purge valve is to create a vacuum on the fuel tank. A minimum duty cycle on the EVAP canister purge valve (75%) must be met before the EVAP Leak Check Monitor can begin.

The Canister Vent (CV) solenoid will close (100% duty cycle) with the EVAP canister purge valve at its minimum duty cycle to seal the Enhanced EVAP system from atmosphere and obtain a target vacuum on the fuel tank.

The Fuel Tank Pressure (FTP) sensor will be used by the EVAP Leak Check Monitor to determine if the target vacuum on the fuel tank is being reached to perform the leak check. Some vehicle applications with the EVAP Leak Check Monitor use a remote in-line FTP sensor. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum for a calibrated period of time will determine if a leak exists.

If the initial target vacuum cannot be reached, DTC P0455 (gross leak detected) will be set. The EVAP Leak Check Monitor will abort and not continue with the leak check portion of the test. For some vehicle applications: If the initial target vacuum cannot be reached after a refueling event and the purge vapor flow is excessive, DTC P0457 (fuel cap off) is set.

If the initial target vacuum cannot be reached and the purge flow is too small, DTC P1443 (no purge flow condition) is set. If the initial target vacuum is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. The EVAP Leak Check Monitor will abort and not continue with the leak check portion of the test. If the target vacuum is obtained on the fuel tank, the change in the fuel tank vacuum (bleed-up) will be calculated for a calibrated period of time. The calculated change in fuel tank vacuum will be compared to a calibrated threshold for a leak from a hole (opening) of 1.016 mm (0.040 inch) in the Enhanced EVAP system. If the calculated bleed-up is less than the calibrated threshold, the Enhanced EVAP system passes. If the calibrated bleed-up exceeds the calibrated threshold, the test will abort and rerun the test up to three times. If the bleed-up threshold is still being exceeded after three tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. This is accomplished by returning the Enhanced EVAP system to atmospheric pressure by closing the EVAP canister purge valve and opening the CV solenoid. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the CV solenoid closes and seals the Enhanced EVAP system. The fuel tank pressure build-up for a calibrated period of time will be compared to a calibrated threshold for pressure build-up due to vapor generation. If the fuel tank pressure build-up exceeds the threshold, the leak test results are invalid due to vapor generation. The EVAP Leak Check Monitor will attempt to retest again. If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 will be set.

If the 1.016 mm (0.40 inch) test passes, the test time is extended to allow the 0.508 mm (0.020 inch) test to run. The calculated change in fuel vacuum over the extended time is compared to a calibrated threshold for a leak from a 0.508 mm (0.020 inch) hole (opening). If the calculated bleed-up exceeds the calibrated threshold, vapor generation is run. If vapor generation passes (no vapor generation), an internal flag is set in the PCM to run a 0.508 mm (0.020 inch) test at idle (vehicle stopped). On the next start following a long engine off period, the Enhanced EVAP system will be sealed and evacuated for the first 10 minutes of operation. If the appropriate conditions are met, a 0.508 mm (0.020 inch) leak check is conducted at idle. If the test at idles fails, a DTC P0456 will be set. There is no vapor generation test with the idle test. NOTE: If the vapor generation is high on some vehicle Enhanced EVAP Systems, where the monitor does not pass, the result is treated as a no test. Thereby, the test is complete for the day.

The Malfunction Indicator Lamp (MIL) is activated for DTCs P0442, P0455, P0456, P0457, P1443 and P1450 (or P446) after two occurrences of the same fault. The MIL can also be activated for any Enhanced EVAP system component DTCs in the same manner. The Enhanced EVAP system component DTCs P0443, P0452, P0453 and P1451 are tested as part of the Comprehensive Component Monitor (CCM) .

 

[sparky2263]

Fuel System Monitor

The Fuel System Monitor is an on-board strategy designed to monitor the fuel trim system. The fuel control system uses fuel trim tables stored in the PCM's Keep Alive Random Access Memory (RAM) to compensate for variability in fuel system components due to normal wear and aging. During closed-loop vehicle operation, the fuel trim strategy learns the corrections needed to correct a "biased" rich or lean fuel system. The correction is stored in the fuel trim tables. The fuel trim has two means of adapting; a Long Term Fuel Trim and a Short Term Fuel Trim. Long Term relies on the fuel trim tables and Short Term refers to the desired air/fuel ratio parameter "LAMBSE". Both are described in greater detail under Powertrain Control Software, Fuel Trim.

Input from the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) , Intake Air Temperature (IAT) , and Mass Air Flow (MAF) sensors is required to activate the fuel trim system, which in turn activates the Fuel System Monitor. Once activated, the Fuel System Monitor looks for the fuel trim tables to reach the adaptive clip and LAMBSE to exceed a calibrated limit. The Fuel System Monitor will store the appropriate DTC when a fault is detected as described below.

The Heated Oxygen Sensor (HO2S) detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air/fuel ratio.

A correction factor is added to the fuel injector pulsewidth calculation according to the Long and Short Term Fuel Trims as needed to compensate for variations in the fuel system.

When deviation in the parameter LAMBSE increases, air/fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the fuel trim table has clipped, the Fuel System Monitor sets a Diagnostic Trouble Code (DTC) as follows: The DTCs associated with the monitor detecting a lean shift in fuel system operation are DTCs P0171 and P0174. The DTCs associated with the monitor detecting a rich shift in fuel system operation are DTCs P0172 and P0175.

The MIL is activated after a fault is detected on two consecutive drive cycles.

 

[sparky2263]

Heated Oxygen Sensor (HO2S) Monitor

The Heated Oxygen Sensor (HO2S) Monitor is an on-board strategy designed to monitor the HO2S sensors for a malfunction or deterioration which can affect emissions. The fuel control or upstream HO2S is checked for proper output voltage and response rate (the time it takes to switch from lean to rich or rich to lean). Downstream HO2S used for Catalyst Monitor are also monitored for proper output voltage. The illustration shows that input is required from the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) , Intake Air Temperature (IAT) , Mass Air Flow (MAF) and Crankshaft Position (CKP) sensors to activate the HO2S Monitor. The Fuel System Monitor and Misfire Detection Monitor must also have completed successfully before the HO2S Monitor is enabled.


The HO2S sensor senses the oxygen content in the exhaust flow and outputs a voltage between zero and 1.0 volt . Lean of stoichiometric (air/fuel ratio of approximately 14.7:1), the HO2S will generate a voltage between zero and 0.45 volt . Rich of stoichiometric, the HO2S will generate a voltage between 0.45 and 1.0 volt . The H02S Monitor evaluates both the upstream (fuel control) and downstream (Catalyst Monitor) HO2S for proper function.

Once the HO2S Monitor is enabled, the upstream HO2S signal voltage amplitude and response frequency are checked. Excessive voltage is determined by comparing the HO2S signal voltage to a maximum calibratable threshold voltage. A fixed frequency closed loop fuel control routine is executed and the upstream HO2S voltage amplitude and output response frequency are observed. A sample of the upstream HO2S signal is evaluated to determine if the sensor is capable of switching or has a slow response rate. A HO2S heater circuit fault is determined by turning the heater on and off and looking for a corresponding change in the Output State Monitor (OSM) and by measuring the current going through the heater circuit. The HO2S Monitor DTCs can be categorized as follows: The Diagnostic Trouble Code (DTCs) associated with H02S lack of switching are DTCs P1130, P1131, P1132, P1150, P1151 and P1152. The DTCs associated with H02S slow response rate are DTCs P0133 and P0153. The DTCs associated with HO2S signal circuit malfunction are DTCs P0131, P0136, P0151 and P0156. The DTCs associated with a H02S heater circuit malfunction are DTCs P0135, P0141, P0155 and P0161. The DTC associated with the downstream H02S not running in on-demand is DTC P1127. The DTCs associated with swapped H02S connectors are DTCs P1128 and P1129.

The MIL is activated after a fault is detected on two consecutive drive cycles.

 

[sparky2263]

Misfire Detection Monitor

The Misfire Detection Monitor is an on-board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The Misfire Detection Monitor will be enabled only when certain base engine conditions are first satisfied. Input from the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) , Mass Air Flow (MAF) and Crankshaft Position (CKP) sensors is required to enable the monitor. The Misfire Detection Monitor is also performed during on demand self-test.


The PCM synchronized ignition spark is based on information received from the CKP sensor. The CKP signal generated is also the main input used in determining cylinder misfire.

The input signal generated by the CKP sensor is derived by sensing the passage of teeth from the crankshaft position wheel mounted on the end of the crankshaft.

The input signal to the Powertrain Control Module (PCM) is then used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria is met, then the suspect cylinder is determined to have misfired.

Misfire type A: Upon detection of a Misfire type A (200 revolutions) which would cause catalyst damage, the MIL will blink once per second during the actual misfire, and a Diagnostic Trouble Code (DTC) will be stored. Misfire type B: Upon detection of a Misfire type B (1000 revolutions) which will exceed the emissions threshold or cause a vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL will illuminate and a DTC will be stored. The DTC associated with multiple cylinder misfire for a Type A or Type B misfire is DTC P0300. The DTCs associated with an individual cylinder misfire for a Type A or Type B misfire are DTCs P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0309 and P0310.

 

[sparky2263]

On Board Diagnostics II Monitors

The California Air Resources Board (CARB) began regulating On Board Diagnostic (OBD) Systems for vehicles sold in California beginning with the 1988 model year. The initial requirements, known as OBD I, required identifying the likely area of malfunction with regard to the fuel metering system. The Exhaust Gas Recirculation (EGR) system, emission-related components and the Powertrain Control Module (PCM) . A Malfunction Indicator Lamp (MIL) labeled CHECK ENGINE or SERVICE ENGINE SOON was required to illuminate and alert the driver of the malfunction and the need to service the emission control system. A fault code or Diagnostic Trouble Code (DTC) was required to assist in identifying the system or component associated with the fault.

Starting with the 1994 model year, both CARB and Environmental Protection Agency (EPA) mandated enhanced OBD systems, commonly known as OBD-II. The objectives of the OBD-II system are to improve air quality by reducing high in-use emissions caused by emission-related malfunctions, reducing the time between the occurrence of a malfunction and its detection and repair, and assisting in the diagnosis and repair of emission-related problems. By the 1996 model year, all California passenger cars and trucks (up to 14,000 lb GVWR) and all federal passenger cars and trucks (up to 8,5000 lb GVWR) are required to comply with either CARB-OBD II or EPA OBD requirements. These requirements apply to gasoline vehicles, diesel vehicles and are being phased in on alternative-fuel vehicles as well.

The OBD II system monitors virtually all emission control systems and components that can affect tailpipe or evaporative emissions. In most cases, malfunctions must be detected before emissions exceed 1.5 times the applicable 50 K- or 100 K-mile emission standards. If a system or component exceeds emission thresholds or fails to operate within a manufacturer's specifications, a DTC will be stored and the MIL will be illuminated within two driving cycles.

The OBD II system monitors for malfunctions either continuously, regardless of driving mode, or non-continuously, once per drive cycle during specific drive modes. A DTC is stored in the PCM Keep Alive Memory (KAM) when a malfunction is initially detected. In most cases the MIL is illuminated after two consecutive drive cycles with the malfunction present. Once the MIL is illuminated, three consecutive drive cycles without a malfunction detected are required to extinguish the MIL. The DTC is erased after 40 engine warm-up cycles once the MIL is extinguished.

In addition to specifying and standardizing much of the diagnostics and MIL operation, OBD-II requires the use of a standard Diagnostic Link Connector (DLC) , standard communication links and messages, standardized DTCs and terminology. Examples of standard diagnostic information are freeze frame data and Inspection Maintenance (IM) Readiness Indicators.

Freeze frame data describes data stored in KAM at the point the malfunction is initially detected. Freeze frame data consists of parameters such as engine rpm and load, state of fuel control, spark, and warm-up status. Freeze frame data is stored at the time the first malfunction is detected, however, previously stored conditions will be replaced if a fuel or misfire fault is detected. This data is accessible with the scan tool to assist in repairing the vehicle.

OBD II Inspection Maintenance (IM) Readiness indicators show whether all of the OBD II monitors have been completed since KAM was last cleared. Ford also stores a P1000 DTC to indicate that some monitors have not completed. In some states, it may be necessary to perform an OBD check in order to renew a vehicle registration. The IM Readiness indicators must show that all monitors have been completed prior to the OBD check.

These descriptions provide a general description of each OBD II monitor. In these descriptions, the monitor strategy, hardware, testing requirements and methods are presented to provide an overall understanding of monitor operation. An illustration of each monitor is also provided. These illustrations should be used as typical examples and are not intended to represent all possible vehicle configurations.

Each illustration depicts the PCM as the main focus with primary inputs and outputs for each monitor. The icons to the left of the PCM represent the inputs used by each of the monitor strategies to enable or activate the monitor. The components and subsystems to the right of the PCM represent the hardware and signals used while performing the tests and the systems being tested. The Comprehensive Component Monitor (CCM) illustration has numerous components and signals involved and is shown generically. When referring to the illustrations, match the numbers to the corresponding numbers in the monitor descriptions for a buffer comprehension of the monitor and associated DTC's.

 

[sparky2263]

Thermostat Monitor

The Thermostat Monitor is designed to verify proper thermostat operation. This monitor will be phased in on certain applications beginning with the 2000 model year and replaces the original "Insufficient temperature for closed-loop test" (DTC P0125). This monitor will be executed once per drive cycle, after a two hour, engine off soak period. If a malfunction is indicated by the thermostat monitor a diagnostic trouble code P0125 will be set and the malfunction indicator lamp will be illuminated.

The monitor checks to see if the engine is being operated in a manner that is generating sufficient heat. While the engine is at moderate load (greater than 30%) and the vehicle is moving (greater than 15 MPH/24 KM ), the Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) should warm up in a predictable manner, therefore, a timer is incremented. The target timer value is based on ambient air temperature at start-up. If the timer exceeds the target time and the ECT or CHT has not warmed up to the target temperature, a malfunction is indicated.

The target temperature will be calibrated to the thermostat regulating temperature minus 20°F (11°C) . For a typical 195°F (90°C) thermostat, the warm-up temperature would be calibrated to 175°F (79°C) .

Inputs: ECT or CHT, Intake Air Temperature (IAT) , engine LOAD (from Mass Air Flow (MAF) sensor) and vehicle speed input.

Output: MIL.

 

[sparky2263]

Powertrain Control Software

Multiplexing
The increased number of modules on the vehicle dictates a more efficient method of communication. Multiplexing is the process of communicating several messages over the same signal path. This process allows multiple modules to communicate with each other through the signal path (BUS +/BUS-). Modules communicate with the powertrain control module using Standard Corporate Protocol (SCP) which determines the priority in which the signals are sent (Refer to Standard Corporate Protocol for more information). Multiplexing reduces the weight of the vehicle by reducing electrical wiring.

Standard Corporate Protocol
The Standard Corporate Protocol (SCP) is a communication language used by Ford Motor Company for exchanging bi-directional messages (signals) between stand-alone modules and devices. Two or more signals can be sent over one circuit.

Included in these messages is diagnostic data that is output over the BUS+ and BUS- lines to the Data Link Connector (DLC) . This information is accessible with a scan tool. Information on this equipment is described in Diagnostic Methods.

Flash Electrically Erasable Programmable Read Only Memory
The Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within the PCM. This IC contains the software code required by the PCM to control the powertrain. One feature of the EEPROM is that it can be electrically erased and then reprogrammed without removing the PCM from the vehicle. If a software change is required to the PCM, the module no longer needs to be replaced, but can be reprogrammed at the dealership through the DLC.

Idle Air Trim

Idle Air Trim Learning Modes Chart






Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in Keep Alive Random Access Memory (RAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output if the Idle Air Trim has reached its learning limits.

Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that Keep Alive RAM be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.

To clear Keep Alive RAM, refer to PCM Reset. It is important to note that erasing DTCs with a scan tool does not reset the Idle Air Trim table. See: Computers and Control Systems\Testing and Inspection\Procedures\Clearing Trouble Codes (PCM, KAM Reset)\With Scan Tool

Once Keep Alive RAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The Idle Air Trim Learning Modes Chart illustration shows different modes.

Fuel Trim
The fuel control system uses the fuel trim table to compensate for normal variability of the fuel system components caused by wear or aging. During closed loop vehicle operation, if the fuel system appears "biased" lean or rich, the fuel trim table will shift the fuel delivery calculations to remove the bias. The fuel system monitor has two means of adapting Short Term Fuel Trim (FT) and Long Term Fuel Trim (FT) . Short Term FT is referred to as LAMBSE and Long Term FT references the fuel trim table.

Short Term Fuel Trim (Short Term FT) (displayed as SHRTFT1 and SHRTFT2 on the scan tool) is a parameter that indicates short-term fuel adjustments. Short Term FT is commonly referred to as LAMBSE. LAMBSE is calculated by the PCM from HO2S inputs and helps maintain a 14.7:1 air/fuel ratio during closed loop operation. This range is displayed in percentage (%). A negative percentage means that the HO2S is indicating RICH and the PCM is attempting to lean the mixture. Ideally, Short Term FT may remain near 0% but can adjust between -25% to +35%.

Long Term Fuel Trim (Long Term FT) (displayed as LONGFT1 and LONGFT2 on the scan tool) is the other parameter that indicates long-term fuel adjustments. Long Term FT is also referred to as Fuel Trim. Long Term FT is calculated by the PCM using information from the Short Term FT to maintain a 14.7:1 air/fuel ratio during closed loop operation. The Fuel Trim strategy is expressed in percentages. The range of authority for Long Term FT is from -35% to +35%. The ideal value is near 0% but variations of ±20% are acceptable. Information gathered at different speed load points are stored in fuel trim cells in the fuel trim tables, which can be used in the fuel calculation.

Short Term FT and Long Term FT work together. If the H02S indicates the engine is running rich, the PCM will correct the rich condition by moving Short Term FT in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time Short Term FT is still compensating for a rich condition, the PCM "learns" this and moves Long Term FT into the negative range to compensate and allows Short Term FT to return to a value near 0%.

As the fuel control and air metering components age and vary from nominal values, the fuel trim learns corrections while in closed loop fuel control. The corrections are stored in a table that is a function of engine speed and load. The tables reside in Keep Alive Random Access Memory (RAM) and are used to correct fuel delivery during open and closed loop. As changing conditions continue the individual cells are allowed to update for that speed load point. If, during the adaptive process, both Short Term FT and Long Term FT reach their high or low limit and can no longer compensate, the MIL is illuminated and a DTC is stored.

Whenever a fuel injector or fuel pressure regulator is replaced, Keep Alive RAM should be cleared. This is necessary so the PCM does not use the previously learned fuel trim values.

To clear Keep Alive RAM, refer to PCM Reset in Diagnostic Methods. See: Computers and Control Systems\Testing and Inspection\Procedures\Clearing Trouble Codes (PCM, KAM Reset)\With Scan Tool

Idle Speed Control Closed Throttle Determination
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned Throttle Position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.

All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts , will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read Closed Throttle (C/T) . Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.

Fail-Safe Cooling Strategy
Only vehicles that have a Cylinder Head Temperature (CHT) sensor will have the fail-safe cooling strategy. This strategy is activated by the PCM only in the event that an overheating condition has been identified. This strategy provides engine temperature control when the cylinder head temperature exceeds certain limits. The cylinder head temperature is measured by the CHT sensor. For additional information, refer to PCM Inputs for a description of the CHT sensor. See: PCM Inputs

A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Along with a CHT sensor, a special cooling strategy is used to prevent damage by allowing air cooling of the engine. The vehicle can be safely driven for a short time with some loss of performance.

Engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When the fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power.

NOTE: A Wide Open Throttle (WOT) delay is incorporated if the CHT temperature is exceeded during WOT operation. At WOT, the injectors will function for a limited amount of time allowing the customer to complete a passing maneuver.

Before injectors are disabled, the fail-safe cooling strategy alerts the customer to a cooling system problem by moving the instrument cluster temperature gauge to the hot zone. Depending on the vehicle, other indicators, such as an audible chime or warning lamp, can be used to alert the customer of fail-safe cooling. If overheating continues, the strategy begins to disable the fuel injectors, a DTC is stored in the PCM memory, and a Malfunction Indicator Light (MIL) (either CHECK ENGINE or SERVICE ENGINE SOON), comes on. If the overheating condition continues and a critical temperature is reached, all fuel injectors are turned off and the engine is disabled.

Failure Mode Effects Management
Failure Mode Effects Management (FMEM) is an alternate system strategy in the PCM designed to maintain engine operation if one or more sensor inputs fail.

When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine operational strategy.

All FMEM sensors display a sequence error message on the scan tool. The message may or may not be followed by Key On Engine Off or Continuous Memory DTCs when attempting Key On Engine Running Self-Test Mode.

Engine RPM/Vehicle Speed Limiter
The Powertrain Control Module (PCM) will disable some or all of the fuel injectors whenever an engine rpm or vehicle overspeed condition is detected. The purpose of the engine rpm or vehicle speed limiter is to prevent damage to the powertrain. The vehicle will exhibit a rough running engine condition, and the PCM will store a Continuous Memory DTC P1270. Once the driver reduces the excessive speed, the engine will return to the normal operating mode. No repair is required. However, the technician should clear the PCM and inform the customer of the reason for the DTC.

Excessive wheel slippage may be caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in rpm while in NEUTRAL or while driving.

 

[sparky2263]

Sorry for the lack of illustrations.

 

[Glacier991]

Excellent! Might want to post the FORD definition of a "drive cycle" if you have that handy. People do not understand how and when a set DTC will disappear....(absent further need for it to continue).

This is a good start on these forums! Thanks!