pcm Imputs
Air Conditioning Cycling Switch
The Air Conditioning (A/C) cycling switch may be wired to either the ACCS or ACPSW PCM input. When the A/C cycling switch opens, the PCM will turn off the A/C clutch. The A/C Cycling Switch (ACCS) circuit to the PCM provides a voltage signal which indicates when the A/C is requested. When the A/C demand switch is turned on, and both the A/C cycling switch and the high pressure contacts of the A/C high pressure switch (if equipped and in circuit) are closed, voltage is supplied to the ACCS circuit at the PCM. Refer to the applicable Wiring Diagram for vehicle specific wiring.
If the ACCS signal is not received by the PCM, the PCM circuit will not allow the A/C to operate. For additional information, refer to PCM outputs, wide open throttle air conditioning cutoff.
NOTE: The Town Car and Continental do not have a dedicated (separate) input to the PCM indicating that A/C is requested. This information is received by the PCM through the BUS + and BUS - (SCP) communication.
A/C Pressure Sensor Output Voltage VS Pressure Chart
Typical Air Conditioning Pressure Sensor
Air Conditioning Pressure Sensor
The air conditioning pressure (A/C pressure) sensor is located in the high pressure (discharge) side of the air conditioning A/C system. The A/C pressure sensor provides a voltage signal to the Powertrain Control Module (PCM) that is proportional to the A/C pressure. The PCM uses this information for A/C clutch control, fan control and idle speed control.
Air Conditioning High Pressure Switch
The A/C high pressure switch is used for additional A/C system pressure control. The A/C high pressure switch is either dual function for two-speed electric fan applications or single function for all others.
For refrigerant containment control, the normally closed high pressure contacts open at a predetermined A/C pressure. This will result in the A/C turning off, preventing the A/C pressure from rising to a level that would open the A/C high pressure relief valve.
For fan control, the normally open medium pressure contacts close at a predetermined A/C pressure. This grounds the ACPSW circuit input to the PCM. The PCM will then turn on the high speed fan to help reduce the pressure.
Typical Brake Pedal Position Switch
Brake Pedal Position Switch
The Brake Pedal Position (BPP) switch is used by the PCM to disengage the transmission torque converter clutch and on some applications as an input to the idle speed control for idle quality. On most applications the BPP switch is hard wired to the PCM and supplies battery positive voltage (B+) when the vehicle brake pedal is applied. On other applications the BPP switch signal is broadcast over the SCP link via another module to be received by the PCM.
On applications where the BPP switch is hard wired to the PCM and stoplamp circuit, if all stoplamp bulbs are burned out (open), high voltage is present at the PCM due to a pull-up resistor in the PCM. This provides fail-safe operation in the event the circuit to the stoplamp bulbs has failed.
Typical Hall-Effect Sensor
Typical Variable Reluctant Sensor
Camshaft Position Sensor
The Camshaft Position (CMP) sensor detects the position of the camshaft. The CMP sensor identifies when piston No.1 is on its compression stroke. A signal is then sent to the powertrain control module and used for synchronizing the firing of sequential fuel injectors. The Coil On Plug (COP) Ignition applications also use the CMP signal to select the proper ignition coil to fire. The input circuit to the PCM is referred to as the CMP input or circuit.
There are two types of CMP sensors: the three pin connector Hall-effect type sensor and the two pin connector variable reluctance sensor.
Typical Clutch Pedal Position (CPP)/Park-Neutral Position (PNP) Switches
Clutch Pedal Position Switch
The Clutch Pedal Position (CPP) switch is an input to the PCM indicating the clutch pedal position and, in some manual transmission applications, both the clutch pedal engagement position and the gear shift position. The PCM provides a 5-volt reference (VREF) signal to the CPP switch and/or a Park/Neutral Position (PNP) switch (on the CPP signal line). If the CPP switch (either or both CPP and PNP switches are closed) is closed, indicating the clutch pedal is engaged and the shift lever is in the NEUTRAL position, the output voltage (5 volts) from the PCM is grounded through the signal return line to the PCM, and there is 1 volt or less. One volt or less indicates there is a reduced load on the engine. If the CPP switch (or PNP switch on vehicle or both CPP and PNP switches open on the vehicle) is open, meaning the clutch pedal is disengaged (all systems) and the shift lever is not in NEUTRAL position (PNP switch systems), the input on the CPP signal to the PCM will be approximately 5 volts . Then, the 5-volt signal input at the PCM will indicate a load on the engine. The PCM uses the load information in mass air flow and fuel calculations.
Three Different Types Of Crankshaft Position (CKP) Sensors
Crankshaft Position Sensor (Integrated Ignition Systems)
The Crankshaft Position (CKP) sensor is a magnetic transducer mounted on the engine block adjacent to a pulse wheel located on the crankshaft. By monitoring the crankshaft mounted pulse wheel, the CKP is the primary sensor for ignition information to the powertrain control module. The trigger wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. The 6.8L ten cylinder pulse wheel has 39 teeth spaced 9 degrees apart and one 9 degree empty space for a missing tooth. By monitoring the trigger wheel, the CKP indicates crankshaft position and speed information to the PCM. By monitoring the missing tooth, the CKP is also able to identify piston travel in order to synchronize the ignition system and provide a way of tracking the angular position of the crankshaft relative to fixed reference.
Cylinder Head Temperature (CHT) Sensor
Cylinder Head Temperature Sensor
The Cylinder Head Temperature (CHT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The cylinder head temperature sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor communicates an overheating condition to the PCM. The PCM would then initiate a cooling strategy based on information from the CHT sensor. 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. Using a CHT sensor and cooling strategy would prevent damage by allowing air cooling of the engine and limp home capability.
Differential Pressure Feedback EGR Sensor
For information on the differential pressure feedback EGR sensor, refer to the description of the Exhaust Gas Recirculation Systems.
Engine Coolant Temperature (ECT) Sensor
Engine Coolant Temperature
The Engine Coolant Temperature (ECT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The ECT measures the temperature of the engine coolant. The sensor is threaded into an engine coolant passage. The ECT sensor is similar in construction to the IAT sensor.
Engine Fuel Temperature (EFT) Sensor
Engine Fuel Temperature Sensor
The Engine Fuel Temperature (EFT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The EFT sensor measures the temperature of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and meter fuel to each engine combustion cylinder.
Engine Coolant Temperature (ECT) Sensor
Engine Oil Temperature
The Engine Oil Temperature (EOT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The EOT measures the temperature of the engine oil. The EOT sensor is similar in construction to the Engine Coolant Temperature (ECT) sensor. On some applications, EOT input to the PCM is used to initiate a soft engine shutdown. This prevents engine damage from occurring as a result of high oil temperature.
Flexible Fuel (FF) Sensor
Flexible Fuel Sensor
The Flexible Fuel (FF) sensor is a capacitive device with a signal processing stage whose frequency varies with the dielectric constant, conductivity and temperature of the methanol-gasoline fuel mixture in its measuring cell. In general, as the percentage of methanol in the fuel mixture increases, the output frequency of the FF sensor signal will increase. For example, a fuel mixture that is 30% methanol will have a FF sensor signal output frequency between 60 and 100 Hz ; 60% methanol will have a FF sensor signal output frequency between 90 and 130 Hz . The PCM uses the percent methanol information to calculate the correct air/fuel ratio and spark advance for the vehicle.
Fuel Level Input
The Fuel Level Input (FLI) is a hard wire signal input to the PCM from the Fuel Pump (FP) module. Refer to the description of the FLI in the On-Board Diagnostics II Monitors.
Fuel Pump Monitor - Applications Using a Fuel Pump Relay for Fuel Pump ON/OFF Control
The Fuel Pump Monitor (FPM) circuit is spliced into the fuel pump power (FP PWR) circuit and is used by the PCM for diagnostic purposes. The PCM sources a low current voltage down the FPM circuit. With the fuel pump off, this voltage is pulled low by the path to ground through the fuel pump. With the fuel pump off and the FPM circuit low, the PCM can verify that the FPM circuit and the FP PWR circuit are complete from the FPM splice through the fuel pump to ground. This also confirms that the FP PWR or FPM circuits are not shorted to power. With the fuel pump on, voltage is now being supplied from the fuel pump relay to the FP PWR and FPM circuits. With the fuel pump on and the FPM circuit high, the PCM can verify that the FP PWR circuit from the fuel pump relay to the FPM splice is complete. It can also verify that the fuel pump relay contacts are closed and there is a B+ supply to the fuel pump relay.
Fuel Pump Driver Module Applications
The Fuel Pump Driver Module (FPDM) communicates diagnostic information to the powertrain control module through the Fuel Pump Monitor circuit. This information is sent by the FPDM as a duty cycle signal. The three duty cycle signals that may be sent are listed in the table.
Fuel Tank Pressure Sensor
For information on the Fuel Tank Pressure (FTP) sensor, refer to the description of the Evaporative Emission Systems.
Fuel Rail Pressure (FRP) Sensor
Fuel Rail Pressure (FRP) Sensor
Fuel Rail Pressure Sensor
The Fuel Rail Pressure (FRP) sensor is a diaphragm strain gauge device in which resistance changes with pressure. The electrical resistance of a strain gauge increases as pressure increases, and decreases as pressure decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to pressure.
Strain gauge type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The FRP sensor measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and meter fuel to each engine combustion cylinder.
The fuel rail pressure sensor senses the pressure difference between the fuel rail and the intake manifold. The return fuel line to the fuel tank has been deleted in this type of fuel system. The differential fuel/intake manifold pressure together with measured fuel temperature provides an indication of the fuel vapors in the fuel rail. Both differential pressure and temperature feedback signals are used to control the speed of the fuel pump. The speed of the fuel pump sustains fuel rail pressure which preserve fuel in its liquid state. The dynamic range of the fuel injectors increase because of the higher rail pressure, which allows the injector pulse width to decrease.
Generator Monitor (Gen Mon)
For information on the generator monitor, refer to the description of the PCM/Controlled Charging System.
Generator Load
The Generator Load Input (GLI) circuit is used by the PCM to determine generator load on the engine. As generator load increases the PCM will adjust idle speed accordingly. This strategy helps reduce idle surges due to switching high current loads. The GLI signal is sent to the PCM from the voltage regulator/generator. The signal is a variable frequency duty cycle. Normal operating frequency is 40-250 Hz . Normal signal DC voltage (referenced to ground) is between 1.5 V (low generator load) and 10.5 V (high generator load).
Heated Oxygen Sensor
The Heated Oxygen Sensor (HO2S) detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a low voltage signal less than 0.4 volt . A low concentration of oxygen (rich air/fuel ratio) produces a high voltage signal greater than 0.6 volt . The HO2S provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. The HO2S generates a voltage between 0.0 and 1.1 volts .
Embedded with the sensing element is the HO2S heater. The heating element heats the sensor to temperatures of 800°C (1400°F) . At approximately 300°C (600°F) the engine can enter closed loop operation. The VPWR circuit supplies voltage to the heater and the PCM will complete the ground when the proper conditions occur. For model year 1998 a new HO2S heater and heater control system are installed on some vehicles. The high power heater reaches closed loop fuel control temperatures. The use of this heater requires that the HO2S heater control be duty cycled, to prevent damage to the heater. The 6 ohm design is not interchangeable with new style 3.3 ohm heater.
Typical Intake Air Temperature (IAT) Sensors
Intake Air Temperature Sensor
The Intake Air Temperature (IAT) sensors are thermistor devices in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The IAT provides air temperature information to the PCM. The PCM uses the air temperature information as a correction factor in the calculation of fuel, spark and MAF.
The IAT sensor provides a quicker temperature change response time than the ECT sensor.
Intake Manifold Runner Control
For information on the Intake Manifold Runner Control (IMRC) , refer to the description of the Intake Air Systems.
Knock Sensor (KS)
Knock Sensor
The Knock Sensor (KS) is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and to retard spark timing.
Typical Mass Air Flow (MAF) Sensor
Diagram Of Air Flow Through Throttle Body Containing MAF Sensor Hot And Cold Wire (and IAT Sensor Where Applicable) Terminals
Diagram of Air Flow through Throttle Body contacting MAF sensor hot and cold wire (and IAT sensor hot wire where applicable) terminals.
Mass Air Flow Sensor
The Mass Air Flow (MAF) sensor uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool. This hot wire is maintained at 200°C (392°F) above ambient temperature as measured by a constant cold wire. If the hot wire electronic sensing element must be replaced, then the entire assembly must be replaced. Replacing only the element may change the air flow calibration.
The current required to maintain the temperature of the hot wire is proportional to the air mass flow. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio. This input is also used in determining transmission Electronic Pressure Control (EPC) , shift, and torque converter clutch scheduling.
Some MAF sensors have Integrated Bypass Technology (IBT) with an integrated Intake Air Temperature (IAT) sensor. The present applications with IBT are: Escort/Tracer (4V) , 2.0L Contour/Mystique, Windstar, Explorer/Mountaineer and 4.2L E-Series.
The MAF sensor is located between the air cleaner and the throttle body or inside the air cleaner assembly.
Power Steering Pressure (PSP) Switch
Power Steering Pressure Switch
The Power Steering Pressure (PSP) switch monitors the hydraulic pressure within the power steering system. The PSP switch is a normally closed switch that opens as the hydraulic pressure increases. The PCM uses the input signal from the PSP switch to compensate for additional loads on the engine by adjusting the idle rpm and preventing engine stall during parking maneuvers. Also, the PSP switch signals the PCM to adjust transmission electronic pressure control pressure during the increased engine load, for example during parking maneuvers.
Power Steering Pressure (PSP) Sensor
Power Steering Pressure Sensor
The power steering pressure sensor monitors the hydraulic pressure within the power steering system. The PSP sensor is a normally closed and opens as the hydraulic pressure increases. The PCM uses the input signal from the PSP sensor to compensate for additional loads on the engine by adjusting the idle rpm and preventing engine stall during parking maneuvers. Also, the PSP sensor signals the PCM to adjust transmission Electronic Pressure Control (ECP ) pressure during the increased engine load, for example during parking maneuvers.
Power Take-Off (PTO) Switch And Circuit To PCM
Power Take-Off Switch and Circuit
The Power Take-Off (PTO) circuit is used by the PCM to disable some of the OBD II Monitors during PTO operation. The PTO circuit normally carries low voltage. When the PTO switch is on/closed, B+ is supplied to the PTO input circuit indicating to the PCM that an additional load is being applied to the engine. If this action was not reported by the PTO circuit, a false Diagnostic Trouble Code may be stored.
Purge Flow Sensor
For information on the Purge Flow (PF) sensor, refer to the description of the Evaporative Emission Systems.
Throttle Position Sensor
The throttle position sensor is a rotary potentiometer or Hall-effect sensor that provides a signal to the PCM that is linearly proportional to the throttle plate/shaft position. The sensor housing has a three-blade electrical connector that may be gold plated. The gold plating increases corrosion resistance on terminals and increases connector durability. The TP sensor is mounted on the throttle body. As the TP sensor is rotated by the throttle shaft, four operating conditions are determined by the PCM from the TP. Those conditions are closed throttle (includes idle or deceleration), part throttle (includes cruise or moderate acceleration), wide open throttle (includes maximum acceleration or de-choke on crank), and throttle angle rate.
Transmission Control Switch (TCS)
Transmission Control Switch (TCS)
Transmission Control Switch
The Transmission Control Switch (TCS) signals the PCM with keypower whenever the TCS is pressed. On vehicles with this feature, the Transmission Control Indicator Lamp (TCIL) lights when the TCS is cycled to disengage overdrive. The operator of the vehicle controls the position of the TCS.
Solid State Relay
For information on the solid state relay, refer to the description of the Secondary Air Injection Systems.
Vehicle Speed Sensor (VSS)
Vehicle Speed Sensor
The Vehicle Speed Sensor (VSS) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/ transaxle shift scheduling and torque converter clutch scheduling.
4X4 Low Touch Drive Button (Switch)
The Generic Electronic Module (GEM) provides the PCM with an indication of 4x4L. This input is used to adjust the shift schedule. A 5.0 volt module pull-up indicates 4x4H or 4x2.
