Time to replace the PCM?

PaulP38a

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New member here, but have found this site to be very useful as an anonymous Googler/reader for the past 18 months we have had a 2002 KJ Limited 3.7L, so thanks so far!

Last week it was running like crap and threw codes P0351 and P0352, indicating a coil problem on 1 and 2.
First thing was a new set of spark plugs. Couldn't get the NGK ZFR6F-11G so got a set of Bosch FR7LCX+ which should be a direct replacement, right?

Reset the fault codes, and started the engine. Still sounded rough and the codes appeared again after a few seconds.

I then swapped the coils around with 3 and 4 to see if the fault followed the coils, but it stayed on 1 and 2.

I bought 2 new Denso coils anyway and put them in. No difference.

Then I spent several hours with the FSM, a multimeter and pen/paper:
  • resistance on all coils, old and new, was in range for both primary and secondary
  • resistance on all spark plugs was in range
  • continuity test on all wires from C1 (1,3,5,7,21) and C2 (9) to the coil plugs was good
  • resistance test on all wires indicated no unwanted grounding. C1-31 and 32 are earth as I recall. Tested with both battery leads removed and all coil leads unplugged, plus C1, C2 and C3 at PCM.
This leads me to think the PCM itself is the problem. Have I missed something?

If you agree it is the PCM, this one is p/n P56041609AF

I see there are a few different models out there. Guessing I can't swap in a P56044xxxyy, but can I use a variant of the P56041xxxyy, P56041609yy or does it have to be the P56041609AF specifically?

Thanks for your time.
 

DadOSix

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New member here, but have found this site to be very useful as an anonymous Googler/reader for the past 18 months we have had a 2002 KJ Limited 3.7L, so thanks so far!

Last week it was running like crap and threw codes P0351 and P0352, indicating a coil problem on 1 and 2.
First thing was a new set of spark plugs. Couldn't get the NGK ZFR6F-11G so got a set of Bosch FR7LCX+ which should be a direct replacement, right?

Reset the fault codes, and started the engine. Still sounded rough and the codes appeared again after a few seconds.

I then swapped the coils around with 3 and 4 to see if the fault followed the coils, but it stayed on 1 and 2.

I bought 2 new Denso coils anyway and put them in. No difference.

Then I spent several hours with the FSM, a multimeter and pen/paper:
  • resistance on all coils, old and new, was in range for both primary and secondary
  • resistance on all spark plugs was in range
  • continuity test on all wires from C1 (1,3,5,7,21) and C2 (9) to the coil plugs was good
  • resistance test on all wires indicated no unwanted grounding. C1-31 and 32 are earth as I recall. Tested with both battery leads removed and all coil leads unplugged, plus C1, C2 and C3 at PCM.
This leads me to think the PCM itself is the problem. Have I missed something?

If you agree it is the PCM, this one is p/n P56041609AF

I see there are a few different models out there. Guessing I can't swap in a P56044xxxyy, but can I use a variant of the P56041xxxyy, P56041609yy or does it have to be the P56041609AF specifically?

Thanks for your time.
Go over your harness carefully. There are a few places that I found rubbed and 'crunchy' on my 04.

Cheaper than a PCM and a good likely culprit.
 

Billwill

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I agree with DadOSix^^^

Physically trace the wires from end to end...unwrap any covering over the harness.

Re-plug the PCM connectors a couple of times to maybe clean the contacts.

Check all the grounds are clean and tight.
Battery Negative Post to chassis must be clean and tight both ends and the Grounding Straps at the rear of the heads going to the Firewall must be clean and tight all ends.;)

The last two Alphabet characters of the PCM PN. ie....xxxxxxxAF are the revision number ie. an xxxxxxxAG would be a slightly newer version....not too important!:)

The Gasser experts here insist that only the Correct NGK plugs should be used!;)

I would personally cut off one of the leads coming off the PCM going to the coil at both ends..a few inches away at both ends and temporarily solder on new a wire to replace the cut-out section and see if that coil now works!;)
 
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PaulP38a

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Go over your harness carefully. There are a few places that I found rubbed and 'crunchy' on my 04.

Cheaper than a PCM and a good likely culprit.
Thanks DadOSix, I know what you mean by crunchy.
Inspected as much of the wiring that I could reach or with a mirror. Looks ok.
If there was a fault I’d expect the continuity or earthing tests would
I agree with DadOSix^^^

Physically trace the wires from end to end...unwrap any covering over the harness.

Re-plug the PCM connectors a couple of times to maybe clean the contacts.

Check all the grounds are clean and tight.
Battery Negative Post to chassis must be clean and tight both ends and the Grounding Straps at the rear of the heads going to the Firewall must be clean and tight all ends.;)

The last two Alphabet characters of the PCM PN. ie....xxxxxxxAF are the revision number ie. an xxxxxxxAG would be a slightly newer version....not too important!:)

The Gasser experts here insist that only the Correct NGK plugs should be used!;)

I would personally cut off one of the leads coming off the PCM going to the coil at both ends..a few inches away at both ends and temporarily solder on new a wire to replace the cut-out section and see if that coil now works!;)

Thanks guys. Do you know what gauge wire I should use by any chance? It’s worth a shot.
That model PCM seems to be very scarce, and then I need to get it programmed with the VIN.
 

Billwill

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Use approximately the same gauge wire as the wire you are replacing.

While that original wire is now "hanging in mid-air" because you cut it off at both ends...place your Ohmeter onto that wire and measure for any conductivity to ground....make sure you are not using bare hands while doing this as it affects the reading.
If you do get some form of resistance reading then this means that the wire is scraping to Ground or to some other random wire!;)

I have replaced about 15 wires using this process after a frontal collision on my 2002 Export Diesel!o_O

If replacing the wire has no effect...solder the original section of wire back in place using Heat-shrink Insulation.;)
 
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Billwill

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Thanks DadOSix, I know what you mean by crunchy.
Inspected as much of the wiring that I could reach or with a mirror. Looks ok.
If there was a fault I’d expect the continuity or earthing tests would


Thanks guys. Do you know what gauge wire I should use by any chance? It’s worth a shot.
That model PCM seems to be very scarce, and then I need to get it programmed with the VIN.

You will also need to program the SKEES code into the PCM to match your Ignition keys if you replace the PCM!;)
 
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PaulP38a

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Use approximately the same gauge wire as the wire you are replacing.

While that original wire is now "hanging in mid-air" because you cut it off at both ends...place your Ohmeter onto that wire and measure for any conductivity to ground....make sure you are not using bare hands while doing this as it affects the reading.
If you do get some form of resistance reading then this means that the wire is scraping to Ground or to some other random wire!;)

I have replaced about 15 wires using this process after a frontal collision on my 2002 Export Diesel!o_O

If replacing the wire has no effect...solder the original section of wire back in place using Heat-shrink Insulation.;)

Many thanks for your advice Billwill. I traced the green/orange wiring back from the 'Coil on Plugs' to pin 87 on the ASD, seeing 12V at pin 2 at all 6 'Coil on Plug' connectors, and verified that disconnecting C112 loses continuity. No earths in these wires.

Also removed, cleaned and replaced the ground points at the firewall and behind the PDC.

Driver wires from the PCM check out ok. tan/red from Coil 1 to C1-7 and tan/pink from Coil 2 to C2-9. Cut and re-joined the wire from C1-7, no change in behaviour. Continuity ok, but still 0V at PCM pin C1-7.

What is curious is that the driver wires for the working coils (C1-1, 3, 5, 21) all show 0.4V at the PCM pins, while the non-working coils show 0V at C1-7, and 0.6V at C2-9.

Think I am going to cut/re-join the wire from C2-9 anyway. What have I got to lose now? :)

It seems that all coils are getting the 12V feed from the ASD but the driver/trigger on pin 1 has failed on 1 and 2.

Presuming that the PCM is stuffed, I took it apart, hoping that maybe there was a dry joint on the dodgy pins. To my surprise, the PCB in the PCM looks very healthy for something with 20+yo components.

Not quite at the point of parting out the KJ and buying my daughter a Camry instead, but close. Guess I will see what a PCM is going to cost, if I can find the right one. Probably less of an issue for our US members, but I don't know if a US spec PCM will function properly in an Australian spec KJ, and then there's the security code issue...View media item 6727
 
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tommudd

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Companies that sell rebuilt ones program them to the VIN, so should be no reason they could not do it for you
 

Billwill

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Can you not get a used PCM from a Breaker Yard?

Just to confirm...when you cut off the two suspect wires at both ends you do get continuity from end-to-end but do you get any resistance reading to Ground at all?

Are you a member of ausjeepoffroad.com?

Maybe someone there has a scrapped Jeep or has a spare PCM or somebody can give you some good advice!;)

You can download the Parts Fiches for the 2002 KJ....usually the PNs will show if there are differences between USA models and Export models and which years have the same PN but probably at this stage it is time to let the Jeep go!:(

www.colorado4wheel.com/manuals/Jeep/KJ/
 

PaulP38a

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Companies that sell rebuilt ones program them to the VIN, so should be no reason they could not do it for you
Thanks Tommudd. Not seeing any matching PCM's on eBay for the P56041609AF model I have.
Is there a shop you guys recommend I could get one from and ship to Australia?
 

PaulP38a

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Can you not get a used PCM from a Breaker Yard?

Just to confirm...when you cut off the two suspect wires at both ends you do get continuity from end-to-end but do you get any resistance reading to Ground at all?
correct, continuity was good on the wires before the cut, and also after the cut/re-join/solder. Not even a micro Ohm showing when doing the ground test with the wires 'hanging'. Gave the wiring harness a bit of a shake while doing this in case it was intermittent.


Are you a member of ausjeepoffroad.com?
I will be shortly, ta :)

You can download the Parts Fiches for the 2002 KJ....usually the PNs will show if there are differences between USA models and Export models and which years have the same PN but probably at this stage it is time to let the Jeep go!:(
That's a good site and where I have already downloaded the FSM and parts fiche for the 2003. Unfortunately can't find the 2002 parts fiche there.
I really don't want to get rid of the KJ. Even with 260,000 KM it drives well and I can see a lot of potential to turn it in to an off road toy for myself when my daughter moves on to another car.
Don't tell anyone, but I have spent years playing with and working on Land Rovers/Range Rovers, and Jeeps are the only other 'proper 4WD' I like :) :)
 

tommudd

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Thanks Tommudd. Not seeing any matching PCM's on eBay for the P56041609AF model I have.
Is there a shop you guys recommend I could get one from and ship to Australia?
Would never buy one from ebay
Been burnt before on parts found on there

Try carcomputerexchange.com
International number 1-919-324-3490
I've used them several times for myself and customers
Gave them the VIN, and when it came it was plug and play, no issues at all
 

Billwill

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correct, continuity was good on the wires before the cut, and also after the cut/re-join/solder. Not even a micro Ohm showing when doing the ground test with the wires 'hanging'. Gave the wiring harness a bit of a shake while doing this in case it was intermittent.



I will be shortly, ta :)


That's a good site and where I have already downloaded the FSM and parts fiche for the 2003. Unfortunately can't find the 2002 parts fiche there.
I really don't want to get rid of the KJ. Even with 260,000 KM it drives well and I can see a lot of potential to turn it in to an off road toy for myself when my daughter moves on to another car.
Don't tell anyone, but I have spent years playing with and working on Land Rovers/Range Rovers, and Jeeps are the only other 'proper 4WD' I like :) :)

The 2003 Parts Fiche is "probably" close enough to the 2003 Parts Fiche.:confused:

"ausjeepoffroad.com" should definitely be able to help you a lot.....not too much traffic there lately on the older KJs but I have found them to be very helpful as regards our RHD Export models and I have helped owners there a few times!;)

I recently made enquires on Ausjeep as regards getting hold of the correct Manual Transmission Oil for my 2002 Export CRD...useless Dealers here told me to use ATF +4 Fluid!:eek:

Someone in the UK saw my post and gave me a link to a supplier back here in SA for German "Ravenol Oils" who supplied me with the correct product...it is a small world with these Interweb things!:)
I also owned a Landrover before I saw the Light and I also drove plenty Landrovers and an old Army Jeep during my Military Service here....loved that Army Jeep which was in showroom condition as it had been stored away since the end of WWII by our Military!;)
 

PaulP38a

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Got a matching PCM programmed with my VIN and security disabled. put it in the KJ today, switched the car on, SKIS light on the dash lights up as usual then goes out. No error codes on the scan tool.
Car won’t crank.

Put the old PCM back in. Same, no crank.

Battery is fine, charged it up for a while anyway. Still won’t crank.

Battery has been disconnected for a week.

Is there something I need to do to ‘reinitialise/relearn’ the old or new PCM?

Just seems weird that I drove the car out of the garage before disconnecting the battery and removing the PCM, and a week later it won’t start at all.
 

Billwill

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Check all the Fuses under the hood.
Swap over the Starter Relay with an identical one nearby.

Remove the Starter Relay and with ignition ON and in "Neutral" and "Park" briefly jumper female pins #30 and #87 together inside the empty socket...engine should at least turn over!;)

If it does not turn over:

Check battery is good....measure across it with Multimeter.
Check battery connections are clean and tight and negative terminal lead going to chassis is clean and tight. The two flexible leads going from the back of the heads are clean and tight on the heads and on the Firewall where they end up!;)

Things seem to have gotten worse since you removed/replaced the PCM!:confused:
 
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PaulP38a

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Check all the Fuses under the hood.
Swap over the Starter Relay with an identical one nearby.

Remove the Starter Relay and with ignition ON and in "Neutral" and "Park" briefly jumper female pins #30 and #87 together inside the empty socket...engine should at least turn over!;)

If it does not turn over:

Check battery is good....measure across it with Multimeter.
Check battery connections are clean and tight and negative terminal lead going to chassis is clean and tight. The two flexible leads going from the back of the heads are clean and tight on the heads and on the Firewall where they end up!;)

Things seem to have gotten worse since you removed/replaced the PCM!:confused:

thanks again BillWill.
Fuses and relays check out ok. Battery and earths are all good.
Jumped the starter relay and also the ASD relay. No attempt to crank over.

Feels like immobiliser, but no light on the dash. Wondering if the VIN is incorrect in the new PCM and that has somehow locked out the old PCM as well when I put it back?

do you know if the body computer plays a part in the immobiliser, and maybe that needs a reset now?
 

Billwill

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Have you joined www.ausjeepoffroad.com yet? I do not see you there!o_O

There could be someone a few blocks away from you who has a few Jeeps in his possession and knows his way around them!

I presume this is an automatic transmission?

You sure you have identified pins #30 and #87 correctly inside the Starter Relay?

If you have downloaded the 2002 KJ Service Manuals then you will see that page 8Wa-21-2 shows that if you jumper pins 30 and 87 together inside the empty Starter Motor Relay slot......+12 volts will go straight through to the Starter Motor via Fuse #4 40A via connector C108 via a Brown wire. So you should be able to measure +12 volts on the Brown wire at the Starter Motor relative to the Starter Motor casing when you briefly jumper those pins together.

Make sure you do not run yourself over while working under the Jeep!!!:eek:

You should hear the solenoid "click" while doing this.

There is a very thick Red wire going onto the large lug on the Starter Motor.
+12 volts should be present there at all times with respect to ground/starter motor casing at all times...even when everything is turned OFF!

Take a thick cable such as from a set of Jumper leads and clamp one end to the Battery Negative post and the other end to the Starter Motor casing and see if the Starter Motor turns over while repeating all the above....if it now turns over then Ground has gone missing on the engine block.

If you do have +12 volts on the small terminal of the Starter motor (Brown Wire) and +12 volts on the large Red Wire at the motor and the motor is not turning over then the Starter Motor has failed or your Battery cannot supply the large current needed!:(
 
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PaulP38a

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Have you joined www.ausjeepoffroad.com yet? I do not see you there!o_O

There could be someone a few blocks away from you who has a few Jeeps in his possession and knows his way around them!

I presume this is an automatic transmission?

If you have downloaded the 2002 KJ Service Manuals then you will see that page 8Wa-21-2 shows that if you jumper pins 30 and 87 together inside the empty Starter Motor Relay slot......+12 volts will go straight through to the Starter Motor via Fuse #4 40A via connector C108 via a Brown wire. So you should be able to measure +12 volts on the Brown wire at the Starter Motor relative to the Starter Motor casing when you briefly jumper those pins together.

Make sure you do not run yourself over while working under the Jeep!!!:eek:

You should hear the solenoid "click" while doing this.

There is a very thick Red wire going onto the large lug on the Starter Motor.
+12 volts should be present there at all times with respect to ground/starter motor casing at all times...even when everything is turned OFF!

Take a thick cable such as from a set of Jumper leads and clamp one end to the Battery Negative post and the other end to the Starter Motor casing and see if the Starter Motor turns over while repeating all the above....if it now turns over then Ground has gone missing on the engine block.

If you do have +12 volts on the small terminal of the Starter motor (Brown Wire) and +12 volts on the large Red Wire at the motor and the motor is not turning over then the Starter Motor has failed!:(

Many thanks for your perseverance on this with me Billwill. Will try your suggestions tomorrow now. Is dark and cold outside here in Canberra.

It is an auto (tested in both P and N), and the ISO micro relay for the Starter Motor has different blade numbers to the 'normal' ISO relays, but the diagram on page 8I-4 of the FSM gave me the mapping.

I am on AusJeepOffroad now and have posted there to see if there are any local enthusiasts who can help solve this riddle.

Kind-of hoping it is the starter motor as I put a new one in back in December so should still be under warranty.

I think this KJ hates me :(:)
 
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Billwill

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Nice to see that you are on ausjeepoffroad now!;)

The Starter Relay that you pull out has the diagram of the pin numbering on the side of the relay...match that to the Female pins in the empty socket to find pins 30 and 87 to briefly short out with a short section of wire. There is also an "87A" contact on the Relay...don't use this one by mistake!

Check that the Brown Wire on the Starter Solenoid does get +12 volts when the Ignition Key is turned to Start...this Brown Wire goes through a Connector C108 which may be disconnected or failing.

You can also take a short lead, fairly thick, and connect it onto the small terminal of the Solenoid on the Starter Motor where the Brown wire is. Leave Ignition OFF, make sure you are in Neutral and Park.

Now briefly touch it to the Positive terminal on the Battery...the Starter motor should turn over if it is not defective!

You may have suffered the problem of the "Broken Actuator Pin Assembly" whereby when you rotate the ignition key a rectangular section of alloy rotates the electrical Ignition Switch.
This Actuator Pin Assembly starts to crumble....it has enough strength to switch on the first positions so Cluster Lights come ON etc. but the final spring-loaded section for Start does not make....a very common problem!

Possibly this Pin Assembly has collapsed a bit more so that the PCM is now not getting power either!:(

If you do get the Starter to turn over by jumpering pins 30 and 87 together inside the empty Starter Relay socket then we can get into how to replace the Actuator Pin Assembly!;)


Edit to Add: Before going any further check Fuse #28 15A inside the PDC again.....if you have jumpered out the wrong pins inside the Starter Relay Socket there is a good chance you have blown that fuse!:(
 
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DadOSix

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Wow!

how did we get from runs poorly to no crank?

maybe starter has a dead spot?

used to tap on the starter a few times with my 73 chevy til I saved enough for a rebuild.
 

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