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Old 09-06-2019, 06:12 AM
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Fried PCM

Dear all,

I have just discovered that my 2.5L 1997TJ has a fried PCM. I bough the car nonrunner, it was only cranking with no start, and no error messages whatsoever. The on-off three times ignition test doesn't turn any error or even the confirmation that it at least checked for error codes
Does anyone have any ideea why the circuit board fried on the top left side of the attached image?

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Old 09-06-2019, 09:14 AM   #2
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Looks like a little fuse soldered in there burnt out. You had a short somewhere on the board.

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Old 09-06-2019, 09:22 AM   #3
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My guess is the black square diode right below it went. You could pull and test it with a multimeter in diode mode
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Old 09-06-2019, 10:10 AM
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Thank you for replying, do you think it could have happened because something else is malfunctioning outside the pcm or it was just a local thing inside the pcm?
I will check that diode as soon as I get home and I will let you know what I find out
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Old 09-06-2019, 01:29 PM   #5
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I’m guessing that when you turn the key on none of the gauges move up. If so you probably have lost the 5v sensor output which results in no start, no spark, no data to the gauges or the OBDII data port (no communication). Most often this shows up on 1997s with the 2.5L for some unknown reason.

If this happens the PCM is almost always the cause. Since you have opened yours & see a bad spot you may be able to repair it. Sometimes leaking capacitors are found which can be replaced.

If this is what is happening & you are able to repair the PCM be sure to post solution. That may help the next guy searching with a similar problem.


If you want to check for 5v supply outputs they are PCM connector C-2 (black) pin 17, orange wire & C-3 (white) pin 31, violet/orange wire.

Before checking this be sure you have 12v key on power to C-2 pin 2 & constant 12v (key off) power to pin 22. And the PCM is grounded from C-2 pins31 & 32.
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Old 09-06-2019, 08:15 PM   #6
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Look on YouTube for Jeep pcm repair. There’s a video of a rather goofy old fellow replacing a cap that looks similar to the photo you posted. He fixed his for a couple of $$.
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Old 09-07-2019, 05:12 AM
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I did those checks, failing to get 5v output made me believe that the pcm is burnt and that is the reason I have opened it. Now I am struggling to identify what was the type of electronic component that burnt, I know where it was located but there was just a pile of Blackburnt matter which when I touched it evaporated.
It is hard to believe that it was a fuse, I would rather think it was a resistor. Does by any chance anybody have an internal diagram of the pcm?
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Old 09-07-2019, 12:09 PM   #8
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I have never seen an internal diagram of any PCM. I’m sure that is a guarded secret.


Are you sure it is not just a jumper or maybe a fused link? If there is no continuity across the 2 ends (looks like not) you could try bridging it to see if it fixes anything. Not much risk if the board is already bad.

Be sure to check the big capacitors shown in the link below. Also you might be interested in reading through it if you have not already done so (while searching).

I also can’t see what, if anything is located in the place where it appears your burnt spot is in the only photo showing that area, unfortunately.

https://www.jeepforum.com/forum/f9/1...rting-2901058/
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Old 09-07-2019, 03:05 PM
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I have some good news, the pcm problem was that it was not able to produce 5v for some sensors and throttle control, idle speed, etc. to work. What i did was to bypass the part of the pcm where it was taking 12v from the battery and transform them to 5v by removing something from the board. The fact is that the pcm has two completely independend 5v generators which goes to orange and purple/orange wires and i have replaced them temporary with 2 cigarete lighter usb chargers 🙂 . Now I can hear the engine running, all the gauges work, and as well i can extract error codes. My engine shuts down imediately after start because of error 25 and i am still looking into this one.
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Old 09-07-2019, 07:07 PM   #10
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I'd just get a new PCM or a used one from a yard. Trouble shooting these are tricky unless a diode,cap, resistor is visually fried. The fuse popped so something isn't right. Might get lucky with a new fuse/ diode but finding the bill of materials for this board is probably impossible. Most of tiny components do not have part #'s on them.
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Old 09-07-2019, 07:16 PM   #11
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The USB charger has successfully been done either for diagnostic (temporary) use or even as a “permanent” solution. I was hoping since you already opened the PCM you might find a solution to actually fixing the PCM.

If you go further on repairing the PCM be sure to post results.



I will post in the other thread about the code 25.
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Old 09-08-2019, 09:40 AM
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Quote:
Originally Posted by VTdirtball20 View Post
I'd just get a new PCM or a used one from a yard. Trouble shooting these are tricky unless a diode,cap, resistor is visually fried. The fuse popped so something isn't right. Might get lucky with a new fuse/ diode but finding the bill of materials for this board is probably impossible. Most of tiny components do not have part #'s on them.
Could you recommend me a place to get one shipped to Europe? What if my problem is outside the pcm and makes it fry?
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Old 09-08-2019, 09:53 AM   #13
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Any auto parts store usb with a 12 volt wired in or cig/power plug usb hub works fine as a 5 volt power source
Power it on with an acc/key controlled 5 volts and use its 5 volt output wherever you need it


Sent from my iPhone using Tapatalk
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Old 09-08-2019, 11:48 AM
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Quote:
Originally Posted by Digger84 View Post
Any auto parts store usb with a 12 volt wired in or cig/power plug usb hub works fine as a 5 volt power source
Power it on with an acc/key controlled 5 volts and use its 5 volt output wherever you need it


Sent from my iPhone using Tapatalk
True but you must disable the 5v on the board if it is shorted as it was my case. The trouble is thst the car doesn't keep the idle...
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Old 09-08-2019, 12:07 PM
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What serial on back of the pcm should I follow to be sure I get on that works on my car?
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Old 09-08-2019, 01:01 PM   #16
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You may have difficulty finding the exact one since you have a European version (EP0 DBB indicates 2.5 engine, manual trans).

From the 1997 parts manual:

56041306AD 1 EP0 DBB After July 24,1997 (EUROPE w/Export Package)

You have AB, the AD indicates an updated replacement version

Here is the US one also EP0 DBB, 2.5 engine, manual trans

56041305AD 1 EP0 DBB After July 24,1997 (FEDERAL/CALIFORNIA)
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Old 09-08-2019, 01:14 PM   #17
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Quote:
Originally Posted by Digger84 View Post
Any auto parts store usb with a 12 volt wired in or cig/power plug usb hub works fine as a 5 volt power source
Power it on with an acc/key controlled 5 volts and use its 5 volt output wherever you need it


Sent from my iPhone using Tapatalk

They need to use a 12v power source which gets power in run & start positions, not run & acc. if you want to start it with the charger’s 5v powering the sensors. Tapping from fuse 9, 10 or 11 in the fuse block is the ideal place for continued use. Or any constant 12v source just for diagnostic purposes.
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Old 09-08-2019, 01:21 PM   #18
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Quote:
Originally Posted by Alexandru View Post
True but you must disable the 5v on the board if it is shorted as it was my case.

True if the PCM is shorted, however, the original idea of using the USB charger was to identify the PCM as the problem by seeing if it would hold the 5v output & the engine would run. Sometimes one of the 3 wire, 5v sensors or their wiring would be shorted & when the charger was put into the circuit the output would go low (even to 0v). Only then isolating the PCM from the circuit(s) would be needed to determine if the short was external to the PCM or internal. So really just a diagnostic tool. If it stays at 5v when just tapped into the 5v circuits (not isolated) & starts you know the PCM is bad & needs replacing.
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Old 09-08-2019, 02:03 PM
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Quote:
Originally Posted by RUBI 4 MY MRS View Post
You may have difficulty finding the exact one since you have a European version (EP0 DBB indicates 2.5 engine, manual trans).

From the 1997 parts manual:

56041306AD 1 EP0 DBB After July 24,1997 (EUROPE w/Export Package)

You have AB, the AD indicates an updated replacement version

Here is the US one also EP0 DBB, 2.5 engine, manual trans

56041305AD 1 EP0 DBB After July 24,1997 (FEDERAL/CALIFORNIA)
I found this one. The seller representative searched my Vin and said that this would be the one for me
https://www.fs1inc.com/engine-comput...m-pcm-oem.html

As well he said that I should check all my wiring for shorted circuit because that is likely to be the problem and install it afterwards

Have you heard about this company in the states or is it a scam?
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Old 09-08-2019, 06:59 PM   #20
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I don't have any personal experience from them. You may want to read through the below thread before placing an order.

https://www.wranglerforum.com/f210/f...l#post34492309
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Old 09-08-2019, 07:54 PM   #21
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Quote:
Originally Posted by Alexandru View Post
I found this one. The seller representative searched my Vin and said that this would be the one for me
https://www.fs1inc.com/engine-comput...m-pcm-oem.html

As well he said that I should check all my wiring for shorted circuit because that is likely to be the problem and install it afterwards

Have you heard about this company in the states or is it a scam?
I strongly recommend that you contact Wrangler Fix instead of FS1.
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Old 09-09-2019, 01:58 AM
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Originally Posted by RUBI 4 MY MRS View Post
The USB charger has successfully been done either for diagnostic (temporary) use or even as a “permanent” solution. I was hoping since you already opened the PCM you might find a solution to actually fixing the PCM.

If you go further on repairing the PCM be sure to post results.





I will post in the other thread about the code 25.
Unfortunately I have managed to make another burn on the pcm. In order to be as explicit as possible I have marked with colored squares few components of the PCM and attached the image.

First when I opened the pcm I have identified an obvious burn on the circuit board, that I have measured and identified it going to black connector into the pcm cav a22 belonging to circuit A14 Rd/wt being described as Fused B+. After a bit of soldering I have closed the circuit, and rechecked the 5v supply output - still not working. So I have opened and noticed that the black integrated circuit marked with Grey square in the attached image was getting hot, so I have disabled the coil marked with red hoping that I have managed this way to bypass the boards transformer. With a bit of measurement I have noticed that the board has two different independent 5v supply so I have replaced the supply with two USB chargers initially soldered straight to to the two capacitors marked with green. The original capacitors seemed fine, but to be sure I have replaced them with brand new ones. When I have measured the voltage on the two 5v wires coming out I could only read 0.6 volts, which was rather odd.. I have then connected the usb straight to the wires. Now I was having 5v, when I put ignition on all the cluster was working and I could fire the engine which was now giving me error code 25.
I then said that maybe because it was shutting the engine down there might be something wrong with the ASD relay. So I have bypassed it. Now the engine was reving using the acceleration pedal but no idle. As soon as it wanted to idle the engine shut down. I really wanted to to hear the engine run so I started it and reved it to 3500-4000range for maybe 8-10 seconds. It was then when the black piece on the board marked with purple and the two fuses next to it burnt and disconnected from the board.
Now I have ordered a new pcm and meanwhile I will check every single wire that the car has.
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Old 09-09-2019, 01:46 PM
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My guess is the black square diode right below it went. You could pull and test it with a multimeter in diode mode
I did test it and was working. To make sure I took it off the board to check it and then soldered it back. That burn you can see in that image is going to a wire that goes all the way at the lights switch
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Old 09-09-2019, 01:49 PM
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Quote:
Originally Posted by Alexandru View Post
I found this one. The seller representative searched my Vin and said that this would be the one for me
https://www.fs1inc.com/engine-comput...m-pcm-oem.html

As well he said that I should check all my wiring for shorted circuit because that is likely to be the problem and install it afterwards

Have you heard about this company in the states or is it a scam?
I strongly recommend that you contact Wrangler Fix instead of FS1.
I did contact them no reply though. Anyway just before I saw the posts here, I had already placed the order with fs1. I will let you know how it turns out

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