Do transmission codes trigger the check engine light?

Dropped the 02 KJ off at a shop due to leaking rear pinion seal. Shop calls me back and says I have transmission codes that impact shifting.

The Jeep does shift with a bit of force at times, but nothing that seems excessive?

I did swap the transmission computer for an 01 Durango unit to convert to 545RFE, part #56028285AH.

I personally drained the transmission fluid with new ATF-4, added a new OEM filter and lube locker. Fluid level has been perfect, no leaks.

Prior to parking it at the shop, I had no check engine light or anything, I even scanned the OBD2 port a few days prior aland nothing showed up.

I can confirm the check engine light does work.

Shop says the codes they found are likely not detectable by a consumer grade scanner.

Is this true?

Yes, it is possible. I have a Bluetooth scanner ($40) and app for my phone that can’t read all the codes that my ($200) Foxwell unit can.

klc said:

Yes, it is possible. I have a Bluetooth scanner ($40) and app for my phone that can’t read all the codes that my ($200) Foxwell unit can.

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Did your codes trigger the check engine light?

You can check yourself if there are codes by following the procedure below:

Without starting the engine, rapidly turn the ignition ON/OFF 3 times.
After the last ON action leave the ignition ON and the Odometer display will show stored codes from the oldest to the latest.

This is for the 02-04 KJs, and I think for the export models like mine, you need to do it 4 times.

Gutzy said:

Did your codes trigger the check engine light?

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I don’t know— I had other issues at the time.

nbas said:

You can check yourself if there are codes by following the procedure below:

Without starting the engine, rapidly turn the ignition ON/OFF 3 times.
After the last ON action leave the ignition ON and the Odometer display will show stored codes from the oldest to the latest.

This is for the 02-04 KJs, and I think for the export models like mine, you need to do it 4 times.

Click to expand...

This is a very, very useful bit of esoterica. Thank you for sharing, and if you have any other tricks please enumerate and share!

I just went through some very weird troubleshooting exercises that were focused on the PCM. Some artifacts included transmission faltering and the AT "slamming" into 2nd. I thought it might be a faulty TCM, so I found an exact part number match on a salvage that was is garage-kept condition, and the problem remained... so it wasn't the TCM.

"I did swap the transmission computer for an 01 Durango unit to convert to 545RFE, part #56028285AH", can you rephrase that? Did you do a trans conversion/replacement? I seem to recall that Durangos can be a v8. If yes, I would strongly recommend that you confirm a part match for a v6. The KJs are proving to be very finicky about matching powertrain/trans modules, especially PCMs to the vehicle VIN.

There are three interrelated components that can affect signals travelling to the TCM from the PCM: Throttle position sensor, Intake Air Control Valve, and Intake Air Temp sensor. A dirty throttle body will also mess up the TCM signals. So remove/clean the throttle body, replace all of those components (reasonably inexpensive, easy reach DIY). ***Do not buy cheapo AMZN parts***. Spend the $ and buy true Mopar. Crown Auto (Quadratec.com) is a good 2nd choise but I still had some touchiness until I installed all Mopar. Besides, new Mopar will last you 150K, anything else is unknown longevity.

I have a 2003 v6 w/ matching 42RLE. If your 2002 v6 is matched to the 45RFE, with VIN-matched TCM and PCM, I would try the 3 parts and throttle cleaning. When I did that, the trans settled back down and runs nice and smooth through the gears. If that doesn't work, here's a pointer to the complete sensor/controller overhaul list: https://www.jeepkj.com/threads/engi...j-2002-2003-and-maybe-2004.80359/#post-811182 . Note that I had a host of misfire and other ghosts in the machine, but the last headache was funky trans shifting and the above mentioned solved the trans problem (after I pointlessly swapped the TCM).

klc said:

Yes, it is possible. I have a Bluetooth scanner ($40) and app for my phone that can’t read all the codes that my ($200) Foxwell unit can.

Click to expand...

is it the elm123 scanner? Does yours run a flash also and have you used that part of it? mine will wright code but I have not been brave enough to test it out

Foxwell NT716. I don’t know if it will flash anything, I bought it because it could show live data.