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ECM/PCM Issue

1

1familyxj

NAXJA Forum User
Location
Gilbert AZ
I have a 98 Cherokee with a 4.0L and an auto trans. I have had issues with the PCM and TCM not communicating for a while now which was causing a check engine light and a P1698 code. I was also experiencing intermittent issues with my fuel gauge not reading and my volt gauge showing 19 volts. Once in a while my check engine light would shut off and my engine would die. It finally died the other day and would not restart. I noticed it will not do the self diagnostic check on the initial key up and the check engine light will not come on at all. I did get the check engine light to come on once and it started and ran. As soon as the check engine light turned off it died again. The only common link I can think of is the PCM/ECM. Any body have any ideas or know a diagnostic test I can run without a scan tool to verify it is the PCM. I have a factory service manual but I will not have access to it for about a month because it is at my parents house. Thank you for any advise.
 
Hey 1familyxj, I also have a 98 Cherokee with a 4.0L and an auto trans. I am also getting the same code, the P1698. The TCM not communicating to the ECM/PCM. I took my XJ to AAmco as I thought it was a transmission related issue. They did a few hours of diagnostics on it, ie wiggle tests continuity tests, ext. They finally came to the conclusion that they were 75% sure it was the PCM/ECM, and 25% sure it was the TCM. They suggested that I replace the PCM first. Well they took forever to get me a price so I searched the internet and found a company called AutoComputerExchange.com. I called and ordered a new PCM from them and am having it 2 day air delivered to me for grand total of $276.95. This includes tax and shipping. The brown Santa is out for delivery as I type this, so as soon as I get off work and replace it, I'll post on here to let you know of my results. It doesnt look to difficult to replace as there are 3 screws and 3 plugs, so I am going to do it myself. When I spoke to the rep she said it is a refurbished or remanufactured unit, I cant remember which. It is programed according to my VIN and the Jeep Part number on my factory unit. She said just plug it in and it will be fine. Hopefully this takes care of the issue and I wish you luck on yours.
 
Thanks for the info. Let me know the outcome. I will probably order from them as well. I found there add on ebay and it looks like I can get it for $245 shipped.
 
I usually steer folks away from AAmoco as they like to sell people trannies even if its a $10 fix. More than likely your PCM and TCM are just fine. Did you try pulling the instrument panel and cleaning the connectors? That's a common problem that can cause communications problems, including an intermittent P1698 code. Other common causes are low battery, bad grounds, or dirty connectors elsewhere.

http://forum.chryslerminivan.net/showthread.php?t=6685
 
I agree. My first job when I moved to AZ was a R&R and tear down tech at an AAMCO. I lasted less than three months before I started seeing how bad they really were. It was my first job out of high school and I learned a lot about what not to do.
 
98XJFLjeeper said:
Hey 1familyxj, I also have a 98 Cherokee with a 4.0L and an auto trans. I am also getting the same code, the P1698. The TCM not communicating to the ECM/PCM. I took my XJ to AAmco as I thought it was a transmission related issue. They did a few hours of diagnostics on it, ie wiggle tests continuity tests, ext. They finally came to the conclusion that they were 75% sure it was the PCM/ECM, and 25% sure it was the TCM. They suggested that I replace the PCM first. Well they took forever to get me a price so I searched the internet and found a company called AutoComputerExchange.com. I called and ordered a new PCM from them and am having it 2 day air delivered to me for grand total of $276.95. This includes tax and shipping. The brown Santa is out for delivery as I type this, so as soon as I get off work and replace it, I'll post on here to let you know of my results. It doesnt look to difficult to replace as there are 3 screws and 3 plugs, so I am going to do it myself. When I spoke to the rep she said it is a refurbished or remanufactured unit, I cant remember which. It is programed according to my VIN and the Jeep Part number on my factory unit. She said just plug it in and it will be fine. Hopefully this takes care of the issue and I wish you luck on yours.
Click to expand...

Did you get your PCM replaced? Did it fix your issue?
 
Have you tried checking eBay or junkyards for replacements? I frequently sell used TCUs on eBay for $25-$50. I believe 1998-2000 all used the same TCU. I don't know about interchange on the ECMs though.

If it were a consistent problem, I'd suggest putting a post up asking if someone in your area would loan you one for a day (yeah we have people on here that generous).

Honestly I'm still a little skeptical that its either computer given the intermittent nature of the instrument panel symptoms. Computers tend to outright die rather than be intermittent. But if you've gone through the wiring and instrument panel then swapping out with known good computers is the next step.
 
Ok, so i got the (new to me) ECm and plugged it in. It said I had a Cylinder one misfire. I plugged the old one back in, and back to normal. So I'm a little upset to say the least. I am going to call them to have them send me another unit, as it seems clear to me that it is faulty. Ill try to go through the connections this week, time permitting with it being thanksgiving and see if I can find a dirty connector or loose one.
 
98XJFLjeeper said:
Ok, so i got the (new to me) ECm and plugged it in. It said I had a Cylinder one misfire. I plugged the old one back in, and back to normal. So I'm a little upset to say the least. I am going to call them to have them send me another unit, as it seems clear to me that it is faulty. Ill try to go through the connections this week, time permitting with it being thanksgiving and see if I can find a dirty connector or loose one.
Click to expand...

So did it run well enough to see if the P1698 code came back?
 
No it didnt run long enough to see the code come back on. I did call the place I ordered the ECM, and they are having me UPS it back to them at there expense, and will ship out another to me. While I am upset about a faulty ECM, I do have to say their customer service has been pleasant. Again, I'll report back with what happens with the next ECM once I receive it.
 
Ok so the new PCM will be here today, but here is somthing strange. I was Going to North Carolina for Thanksgiving. On my 10 hour drive north, the alternator went out on the Jeep. I bought a new one and replaced it on Friday, and the Jeep is no longer throwing any codes. It has done this since Friday and here it is Tuesday, and I have driven about 1,000 miles since I changed it. I would expect it to come back on had the PCM been the actual problem.
 
I'm not sure how it would be directly related, but low voltage or poor grounds can cause all kinds of wierd things. Might have fixed one of those problems.
 
I am waiting for my new ECM to arrive. As soon as mine gets here I will post up and let you know what the outcome is. I would be real surprised if my problem is anything other than the ECM.
 
Well, my new ECM will be here today, I am not having the problems anymore, so I am wondering if I should replace the old with the new. Would a new one have updated software that would be better for the Jeep? Would there be any benefit to using the refurbished one?
 
The new ECM should have the latest updates. Chrysler corporation comes out with flash updates to take care of any glitches they find in the ECM. I would install the new ECM if it were me but it is your money and your Jeep. I hope your problems with your Jeep are resolved so you can go wheeling. I know I miss driving my jeep. I can't wait to get it fixed. I am jonesing to go wheeling!
 
98XJFLjeeper said:
Well, my new ECM will be here today, I am not having the problems anymore, so I am wondering if I should replace the old with the new. Would a new one have updated software that would be better for the Jeep? Would there be any benefit to using the refurbished one?
Click to expand...

I had done a similar thing when I ordered mine for my 97. I ended up discovering after putting in the new PCM that it was not the problem, but I kept my new one anyway because she runs so good now, I don't want to risk that by going back to the old PCM. Besides, the new one has been flashed with all updates relative to my specific VIN, and I have a lifetime warranty. Once I have something I like, it's hard to let go of it, so I kept it.
 
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