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Ford Explorer PCM Power Procedure

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Old 01-11-2010, 08:12 PM   #1
2000StreetRod
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Ford Explorer PCM Power Procedure

Background

The powertrain control module (PCM) receives information from engine and vehicle sensors and controls the fuel injection, ignition timing, exhaust gas recirculation and automatic transmission. It's functionality is essential to the operation of the vehicle. Without power, the PCM is unable to perform its designed capabilities. This procedure was generated to determine if the PCM is receiving power and if it is not to assist with correcting the situation.

According to the Owner's Guide the "CHECK ENGINE" light should illuminate when the ignition switch is turned to On to test that the bulb is good. If the light was functioning normally earlier then it is likely that the PCM no longer has power. If the light was not functional earlier then the current power state of the PCM is unknown.

Procedure

1. Check the voltage between the battery posts. A fully charged battery should indicate a voltage of about 12.6 volts. If the battery voltage is low charge or replace the battery.

2. Check the condition of the battery cables and connectors. Clean and tighten connectors if required.

3. For year 2000 the main power for the PCM comes from Fuse 10 (30 amps) via the PCM Power Relay which are both located in the Battery Junction Box. For year 1996 the main power for the PCM comes from Fuse 13 (30 amps) via the PCM Power Relay which are both located in the Power Distribution Box. Check the Fuse at both ends for battery voltage at all times. If the fuse is blown replace it.

4. There is a separate power path for the PCM volatile memory called keep alive memory (KAM). For year 2000 the KAM power comes from Fuse 6 (10 amps) located in the Battery Junction Box. For year 1996 the KAM power comes from Fuse 4 (20 amps) located in the Power Distribution Box. Check the fuse at both ends for battery voltage at all times. If the fuse is blown replace it.

5. The PCM Power Relay control solenoid receives power from the PCM Power Diode located in the Battery Junction Box for year 2000 or the Power Distribution Box for year 1996. Check the diode at both ends for battery voltage when the ignition switch is in On and Start. If the diode is blown replace it. If the diode passes the battery voltage test then go to the next numbered step.

If battery voltage is not at the diode then check it's source which is Fuse 19 (25 amps) located in the Central Junction Box. Check the fuse at both ends for battery voltage when the ignition switch is in On and Start. If the fuse is blown replace it. If the fuse passes the battery voltage test then go to the next numbered step.

Fuse 19 gets power from the Ignition Switch. For year 2000 the ignition Switch receives power from Fuse 5 (50 amps) located in the Battery Junction Box. For year 1996 the ignition Switch receives power from Fuse 1 (60 amps) located in the Power Distribution Box. Check the fuse at both ends for battery voltage at all times. If the fuse is blown replace it. If the fuse passes the battery voltage test then go to the next numbered step unless there is still not battery voltage at Fuse 19 when the Ignition Switch is in On or Start. Otherwise, check the yellow wire and light green/purple wire connections to the Ignition Switch and replace the Ignition Switch if required.

6. The easiest and quickest method to check the PCM Power Relay is by substitution. Disconnect the battery cable from the negative post. Pull the PCM Power Relay from the Battery Junction Box and set it aside. Pull the Blower Motor Relay from the Battery Junction box and insert the pulled relay into the PCM Power Relay position. Reconnect the battery cable. Turn the ignition key to On and see if "CHECK ENGINE" is illuminated.

7. If the "CHECK ENGINE" is not illuminated the light may be burned out and the PCM may actually have power. A fairly easy way to check is to test the TPS reference voltage generated by the PCM. Connect the positive probe of a voltmeter to the brown/white wire at the TPS connector. Connect the negative probe of the meter to the gray/red wire at the TPS connector. With the Ignition Switch in On the meter should measure at least 4.0 volts confirming PCM power.

Last edited by 2000StreetRod; 03-20-2010 at 09:02 AM.
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Old 08-12-2011, 09:59 AM   #2
Kravist
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Suggest One Change To The Procedure

I have a suggestion regarding this procedure.

Perform Step #7 first. If you are getting 4 VDC at the Throttle Position Sensor (TPS), your Powertrain Control Module (PCM) is getting power and providing outputs -- so you can move on to Engine No Start Procedure Step #4.

My background is that I was an aircraft electrician in the US Marines.

The only reason I make the suggestion is that by checking that output (the TPS voltage) from the PCM -- we are confirming what the extinguished Check Engine Light (CEL) is telling us: the PCM is not providing an output.

If your CEL and/or wiring is faulty, we are eliminating a big chunk of troubleshooting in less than 2 minutes.

As I said in a related thread... This guide from 2000StreetRod is fantastic.
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Old 04-28-2014, 06:36 PM   #3
gregoryll
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I have a similar problem with a 1995 Ford Explorer 4.0. Put new wires and plugs in it the other day, it started up fine. About an hour later I was driving it, hit some bumps and the vehicle died. It hasn't started since. On a whim I replaced the crank position sensor, still won't start. So today I start checking fuses, # 13 in the power distribution box was blown, # 19 in the interior fuse box was blown. I replaced # 13, when I replace # 19 it blows immediately.

Is it common for a vehicle this old that is used primarily on bumpy dirt roads, to ruin the PCM?

I will check the relay, or switch it with one of the others and check for broken wires and see what I find.

Any advice would be greatly appreciated.

Thanks for reading.
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Old 04-28-2014, 08:58 PM   #4
2000StreetRod
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Fuse 19

Fuse 19 in the interior fuse panel provides power to the PCM Power Relay via the PCM Power Diode, to the radio noise suppression capacitor, and to the ignition coilpack. The PCM gets power from PCM Power Relay. I suggest pulling the PCM Power Relay, and disconnecting the connector to the coilpack and the radio noise suppression capacitor. Then replaced fuse 19 and see if it still blows with the ignition on. If it does, then there is a short to ground in the wiring. If it doesn't then there is a short to ground in one of the three components mentioned above. Next install the PCM Power Relay and turn the ignition on. If fuse 19 blows then replace the PCM Power Relay. If it doesn't blow then connect the coilpack connector and try the ignition on again. If fuse 19 still doesn't blow then try starting the engine. The radio noise suppression capacitor can fail in a shorted mode. You can drive the vehicle without one but the radio may pick up some ignition noise.
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Old 06-05-2014, 05:58 AM   #5
asalasch
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Great info!!
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Old 06-08-2014, 03:35 PM   #6
Betsy98Sport
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Quote:
Originally Posted by 2000StreetRod View Post
Fuse 19 in the interior fuse panel provides power to the PCM Power Relay via the PCM Power Diode, to the radio noise suppression capacitor, and to the ignition coilpack. The PCM gets power from PCM Power Relay. I suggest pulling the PCM Power Relay, and disconnecting the connector to the coilpack and the radio noise suppression capacitor. Then replaced fuse 19 and see if it still blows with the ignition on. If it does, then there is a short to ground in the wiring. If it doesn't then there is a short to ground in one of the three components mentioned above. Next install the PCM Power Relay and turn the ignition on. If fuse 19 blows then replace the PCM Power Relay. If it doesn't blow then connect the coilpack connector and try the ignition on again. If fuse 19 still doesn't blow then try starting the engine. The radio noise suppression capacitor can fail in a shorted mode. You can drive the vehicle without one but the radio may pick up some ignition noise.
Not sure how to finish your procedure. Can the radio capacitor cause 19 to blow? Second question is can the radio capacitor cause the ignition coil to fail if it's bad?
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