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Ford Explorer PCM Power Procedure

Discussion in 'Under the Hood' started by 2000StreetRod, January 11, 2010.

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    1. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      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: March 20, 2010
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    3. Kravist

      Kravist New Member

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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.
       
    4. gregoryll

      gregoryll New Member

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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.
       
    5. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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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.
       
    6. asalasch

      asalasch New Member

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      Great info!!
       
    7. Betsy98Sport

      Betsy98Sport Active Member

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      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?
       
    8. tarrakas

      tarrakas New Member

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      Hate to bring up a dead thread, but I'm experiencing this issue as well. Was curious where these components are grounded, and what the best course of action would to resolving the grounding issue. (As in repair the existing faulty ground or installing a whole new one.)
       
    9. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      which components?

      Which components are you referring to? Also, which of your vehicles has the problem?
       
    10. tarrakas

      tarrakas New Member

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      Well, to be more specific, its the 95 explorer giving me trouble. And to clarify my question, how are the coils, the PCM, and the radio noise grounded. Also, while attempting to find my fault, I tested the actually plug for the fuse (#19 in the drivers side panel) and got a drop of about .3. I came to this conclusion by inserting the propes into the slots, then testing the negative against the frame. Is this my fault? Or am I just ignorant to the proper use of the meter and electrical cucuits?
       
    11. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      ignition related grounds

      The wiring diagrams I have access to don't identify the ground location for the ignition coil or the radio noise capacitor.
      Ignition95a.jpg
      Normally the secondary of the ignition coil is grounded thru the bolts that mount the coil. The primary is grounded by the circuits in the ignition control module. The ground end of the radio noise capacitor should have a wire that is either connected to a firewall stud or a stud on the engine. The ground connections can become corroded after 20 years so it might be a good idea to clean them by scraping.
      Ignition95b.jpg
      The PCM power relay is grounded by G100 which is a common ground for numerous devices.
      Ignition95c.jpg
      I don't understand where you measured the 0.3 volt drop but that is not unreasonable for 10 feet of wire and connections.

      What are your ignition related symptoms?
       
    12. tarrakas

      tarrakas New Member

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      Well, she'll fire right up as if nothing is wrong. For the most part she runs, but she keeps blowing fuse 19. Then its crank but no fire. ( no power to the coils, duh). After it pops 19, sometimes I can simply replace it, other times it will immediately blow the fuse again and I have to let it sit. I've only owned the explorer for about a week and a half, so I don't have a complete history for the vehicle.

      When I bought my ranger many years ago, it too was used and in need of some serious work. After it was all said and done, its been the singleost reliable vehicle in the family, outlasting many other more modern and expensive cars. I'm confident that if I can solve this electrical problem, this too will be an outstanding vehicle. (That, and the ball bearings I'll be replacing ASAP)
       
    13. cj111

      cj111 New Member

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      Even though this is a Old post, this may or may not help you. I have a 95 ford explorer sport 4.0 ohv 4x4. I have done several test and replaced almost every part on it, including head gaskets and up. The converter was plugged ( 1st one , second one was clean )This may be from using standard spark plugs ( see AA1Car.com for info, and EasyAutoDiagnostics.com for testing) instead of the Iridium. Have had several problems back and forth until I changed out old valve body in trans to the updated valve body and plate. The old one had a Transgo kit installed for a 4R55e trans that it has , but the old valve was worn out and not worth playing with. I have had a new computer put on, the old one was a ARC, but the ford tsb calls for the BRA or newer BSA updated computer if the Ford valve body has been done.Still had some small issues with power performance and slow learning issues for proper shift patterns and kickdown settings. At one time the overdrive would kick in and the rpms would be 1200 at 50 miles per hour, which is nice except that I was getting 6 1/2 miles per gallon( not good ). Then I changed the Air Charge Sensor and the water temp gauge responded quicker even at 0 degrees outside. Now keep in mind that I have done the test as according to the postings stated at forums and testing sites that provide this info. Now the mileage went up to 10 mpg and overdrive now kicks in at 1400 rpms at 50 mph. But finally I thought this still is not right another ICM even though I think the Original is still good and the test prove this out but so did the test on the Air Charge Sensor. Then I decided to test the voltage at the PDC box under the hood and the PCM diode and the connections to it along with the relay.PCM diode is good so is the relay. Then I tested the ends of the fuses with the car running and was getting 11.64 volts at each side of the fuse on all the PDC fuses, Maxi and Mini. Then I checked all the interior fuses in the car at the interior fuse block and they are all providing 14.64 volts with the car running. Strange the PDC supplies the current to the interior box and it's voltage is less. WHY?. So being that this car is more stubborn then a mule doing the quarter mile running backwards drinking a smoothie made of straw, I removed the alternator and went to AutoZone and had them test the alternator. I found out like they did that the unit was putting out 14.5 to 14.8 volts under load. and at non load I had 14.87. But when they put it on the machine it passed the ripple test,volts, lamp/in but not the lamp/out test. The reason was given that a diode was bad so the Alternator must be bad. So thinking that this still does not fully explain the voltage difference I went home and disassembled the Alternator and carefully looked for any broken wires and or short. Then I tested the diodes and they showed good. So I cleaned the unit with Electrical cleaner and was about to reassemble the unit when I noticed a grove cut in the inner brush location on the armature from the voltage regulator brushs. After watching a video on youtube by a guy in Canada davesfarming or something about the description of a alternator, he says that the inner location is the negative feed I Guess to diodes. I continued to assemble the unit and reinstall. I then started the car and had the volt meter ready and PDC box open. The first test gave a reading of 13.64 and I reved the engine to 2000 rpms , let it idle then shut it off. I then restarted the car and retested and now I have 14.64 volts the same as the interior fuse box. Not sure if this voltage should be this high as there are no post that I can find telling what the voltage should be as the car is running. I did take it out for a road test and right away I could feel the differnece in engine performance and i shifting. It was like a new car responding that has 160,000 miles on it.The sluggish performance returned for 30 secs and then went away but the fuel mileage problem seems to be getting better, not positive yet on that one. Ordered a new 130 amp Alternator for it with a new TPS and EVAP solenoid ( the one that mounts on the front axle )and has the connection for the 4x4.The old alternator does not have " ANY " ford numbers or any other number on it ( strange ). The car has everything but heated seats so might as well step up the amps from a possible 95 amp old one.Only thing left on the car is the coil pack but if test prove ok why replace it. Well maybe the mule has got the wrong spark going to the wrong places that why she learns as slow her computer crank and that is really slow.Well maybe someone else may have this problem and maybe this might help, and maybe your mule has a better learning curve, and she gets there quicker...The water temp sender is new and also the the sending unit for the water temp gauge and has never been a problem, this eliminates any malfunction in the sensors to PCM for cold starts and should not be a factor in the proper fuel usage. The DPFE sensor works as according to the test from EasyAuto Diag. I purchased a new one from amazon for a Standard VP12 I believe and amazon says it will not work and RockAuto says this is the one. Square connector with cut off corners. The part number matched up with the Alternate numbers given at rockauto and Standards site from the original one on the car ( metal DPFE). It would not work readings did not match up and thus the EGR/PCM did not work properly. Reinstalled the old unit and all the readings are perfect. This may again be caused from the " LOW VOLTAGE " feeding the supply, but again the test prove out ok. I think what might be according is that the Negative feed on the inner brush location on the Armature in the Alternator is hanging up in the worn grove it has created and overheating the carrier that holds the brush in place and short circuiting the voltage at different intervals and causing faluts in either the relays or PCM fuel injection driver or the ICM that feeds the PCM fuel injection drivers, then that would explain the variables in engine performance and transmission shift performance. When I have installed the New alternator and rechecked the new ICM and verified voltage at all the fuses and test to see if the voltage is the same then maybe I might purchase new plugs again just in case these plugs may some how have built up a resistance from the voltage supply. This has been a easy project to work on, it's been a little nerve racking retesting the same part over and over but maybe this can finally be on the way to a full recovery, Damm mule !!!!...best of luck ..cj
       
      Last edited: December 16, 2015
    14. pierceve

      pierceve New Member

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      So how is the old mule doing was this the fix? I have been experiencing the same issue with the volts showing 11.64. Thank you for any reply in advance
       

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