99 PCM replace/update
#1
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From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
99 PCM replace/update
So I've recently taken the jeep in for diagnostic of p1391 throwing a CEL every second start after clearing it.
Cam crank sensors are synced, signal gets to PCM, jeep starts, runs, and drives fine.
The diagnostic shows everything running cleanly.
They suggest maybe having a dealer trying to update mine before replacing it.
My question is what do I need to be concerned with as far as this goes, they kept saying a new computer needs to be programmed?
Cam crank sensors are synced, signal gets to PCM, jeep starts, runs, and drives fine.
The diagnostic shows everything running cleanly.
They suggest maybe having a dealer trying to update mine before replacing it.
My question is what do I need to be concerned with as far as this goes, they kept saying a new computer needs to be programmed?
#2
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Yeah they say programmed, all it is is they put in the mileage and the vin number. They are not updateable in terms of the programming they run.
#4
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Not sure I understand your question because you only said "They suggest maybe having a dealer trying to update mine before replacing it."and then I said "Programmed" which I should have said "update". But as far as I know, if your profile is correct and we are talking a 99 xj,
By the way, who is "they"?
The only info I know of that the pcm will take is the vin and mileage. I'm not 100% on that. But I do know that the 96 and 97 zj does not even need that, when you buy a pcm it's just plug it in and go, because the vin and mileage are stored in the bcm. Regardless of that, many sellers of pcm's will still insist in their advertising that you must provide that info so they can "flash" or "program" the new pcm.
I don't think in 99 they were as sophisticated as a new Iphone that needs operating system updates. Not to doubt the word of a DEALER who this site knows so well, are always so honest, correct, skilled, trained and informed.
By the way, who is "they"?
The only info I know of that the pcm will take is the vin and mileage. I'm not 100% on that. But I do know that the 96 and 97 zj does not even need that, when you buy a pcm it's just plug it in and go, because the vin and mileage are stored in the bcm. Regardless of that, many sellers of pcm's will still insist in their advertising that you must provide that info so they can "flash" or "program" the new pcm.
I don't think in 99 they were as sophisticated as a new Iphone that needs operating system updates. Not to doubt the word of a DEALER who this site knows so well, are always so honest, correct, skilled, trained and informed.
Last edited by 97grand4.0; 06-13-2019 at 07:39 PM.
#5
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Year: 96
Model: Cherokee (XJ)
Engine: 4.0
there is an attached youtube on fixing jeep with this code!,,, didnt view it
#6
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From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
Sorry, "they" the shop I got to run the diagnostic, suggested having the dealer try updating my 99 PCM. If that didn't work they said the dealer would still have to do something to a replacement PCM.
I guess a pcm can't be flashed by a shop? Idk, he said they couldn't.
I guess a pcm can't be flashed by a shop? Idk, he said they couldn't.
#7
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From: PA
Year: 1997
Model: Cherokee
Engine: 4.0L
The only time i have heard of a PCM in an XJ needing "programmed" is when you add or remove SENTRY, which is pretty much all you can do with them. Aside from that we are stuck with whatever was programmed into them from the factory. I would like to think that if one could do more, the forums would be loaded with threads from those that have had it done. If they have, they are being awfully quiet about it.
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#8
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From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
https://autoservicecosts.com/obd2-codes/p1391/
there is an attached youtube on fixing jeep with this code!,,, didnt view it
there is an attached youtube on fixing jeep with this code!,,, didnt view it
The diagnostic results a lab scope showing ckp,cmp are in sync. This also showed signal being received at the pmc and the pmc continuing to set the code. A skipped tooth is very very very unlikely with this engine and also would result in a sync issue.
The harness has great continuity to pcm. Grounds are good, voltage and signal are strong. With this and sensors reading properly, replacing them is not a logical step. This is again where the PCM having an issue comes into play and is as the shop said 99% the culprit.
Is there any pcm testing a dealer can do to see if this is absolutely the case? Other wise can I just grab a 99 PCM from the JY and be on my way?
#9
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Year: 96
Model: Cherokee (XJ)
Engine: 4.0
The diagnostic results a lab scope showing ckp,cmp are in sync. This also showed signal being received at the pmc and the pmc continuing to set the code. A skipped tooth is very very very unlikely with this engine and also would result in a sync issue.
Is there any pcm testing a dealer can do to see if this is absolutely the case? Other wise can I just grab a 99 PCM from the JY and be on my way?
Is there any pcm testing a dealer can do to see if this is absolutely the case? Other wise can I just grab a 99 PCM from the JY and be on my way?
I dont think it matters that much if the VIN is not correct, my 3 x '96 models, the reader will not detect the VIN anyway
For the price of a PCM from a wrecker?Ebay, its probably worth a try...I would make sure the part num on the PCM matches...plenty on Ebay
#11
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Cause IMO you need to clear the Adaptive Memory.
Also IMO I sincerely doubt that the only symptom of a bad ECU is it forgot what the camshaft voltage should be.
Also IMO I sincerely doubt that the only symptom of a bad ECU is it forgot what the camshaft voltage should be.
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Year: 96
Model: Cherokee (XJ)
Engine: 4.0
I own a '03 GM Commodore with Alloytec motor...they are known to have this issue
If P1391 means "detecting CMP and CPS out of sync" ..they probably are!
It would be cheaper to put a used PCM in it, if that doesnt work, onto the next thing
#15
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Try this one:
https://www.jeepforum.com/forum/f67/...emory-1265118/
Forced Flash
This very simple procedure will Erase the “Adaptive Memory” stored inside the TJ PCM and allow a new “Adaptive Memory” to be developed.
After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.
[L]Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.
Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”[/L]
Adaptive memory has nor been flashed, or erased from the PCM.
When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.
When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.
The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
This very simple procedure will Erase the “Adaptive Memory” stored inside the TJ PCM and allow a new “Adaptive Memory” to be developed.
After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.
[L]Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.
Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”[/L]
Adaptive memory has nor been flashed, or erased from the PCM.
When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.
When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.
The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.