Transmission Limp Mode

Roy,

Thank you for getting back to me. I'm writing you from Sofia, Bulgaria, pretty much halfway around the world where we don't have shops for American cars.

Here's the chronology of events:

1. Car went into limp mode (stuck in 2nd gear) summer of 2020. It would go in and out of it occasionally but most of the time it would stay in limp mode. Only visible issue was that at times, mostly when the car was cold, all positions of the lever were marked active on the dash (squares around every letter) so we started by replacing the neutral position switch inside the transmission. That did not resolve the issue.

2. We took the car to at least three other shops one of which specializing in automatic transmissions. Relevant DTC was P0700 (the non-specific one) so all shops backed out saying they didn't know how to approach the issue and that it could be anything.

3. I spent months reading forums and found a small number that said these transmissions are extremely sensitive on the exact transmission fluid they're designed for which is Mopar ATF+4. We went out on a limb and did a service change air-forcing as much as possible of the current fluid out to finally change around 60% of the whole quantity. ATF had never been changed prior on this vehicle. This fixed the problem. Car drove fine for about 300 miles for a month. Then limp mode again.

4. We figured the remaining old fluid could cause the issue to come back so we did a second service change (a full flush would cost a fortune compared to the price of the car), so we expected to at least have a temporary result like the first time. No luck. Car never even went out of limp mode this time.

5. We took a wild guess that maybe while shuffling stuff around we caused an electrical line to go on and off. We looked into electrical and found out solenoids could be the issue as they're connected to the TCM (integrated with the PCM.) We replaced the solenoid block. The problem persisted.

6. On yet another testing session I personally wiggled around the solenoid connector. This fixed the problem. For another couple of days. Then out of nowhere limp mode again. This led us to the wiring harness. We took it all out and tested each wire with a stress test, pulling, twisting and pushing. All were fine. Not a twitch on the voltmeter. And no further wiggling of wires resolved anything.

7. We found there was a broken safety clip on the second big connector there, the one for the neutral position switch. We tightened the female pins to secure contact. Nothing changed.

8. We took the car in for another read and it no longer brought back the P0700. Only DTC that could be relevant is now P0211 and as much as I read about it, I don't see how it can be related to the transmission limp mode.

This is about where we are. I'm doing this with my dad (78) as this is his car and now they can barely go shopping in it.

I'd appreciate it tremendously if you could help me make some sense of all this and point me to what I could be missing. The issue has been so random during the past year that I'm out of ideas already. I'm thinking if the mechanic connected the neutral safety switch inside correctly. How could he go wrong though?

Thank you for your time.

Krassimir Stoichev

Joe,

Thank you for getting back to me. No, no progress since my detailed description.

CAN was scanned and not a single TCM code was found stored. That's unlike prior attempts as described which brought back the P0700. Now transmission system reads healthy and it's not.

Please follow through the events and try to make up a logical chain and direct me to what you would do in the circumstances. They won't get any clearer right now. Otherwise I wouldn't be so lost myself. :)

Thank you.

Joe,
Roy,

Thanks for the follow-up. First of all, we're in a part of the world where American cars are extremely rare and so are their diagnostics. We can barely find a shop to read the DTCs here. In Europe we don't use scan tools, instead we use just software that reads live and stored data via OBDII connection to a laptop computer. That's now we got what we got.

Needless to say, testing sequences are not at all like what's described in the service manual. And what's even worse, we do not have diagnostic software of our own. Each time we test we have to book with a shop and they're not very attentive at all. They basically rush through the DTCs because we don't book a repair with them, only diagnostics and they don't make that much money off this.

We've done DTC reads four times now and up until the last time the P0700 was stored but no other transmission-related code was stored or would come up live. That's why we don't have a clue, hence this thread.

NB! Joe, no, replacing the TRS never resolved the dash lever position issue. It pops up randomly still. A question on this one: what's the connection of the TRS inside the gear box and could it be compromised? I'm thinking, if a signal to the outside connector is lost this could cause this behavior and the limp mode but is it worth investing into opening up the transmission again to check how the TRS is connected inside? How possible is that?

The P0211 is exactly what it is, no error there. I also thought it wasn't related but had to ask. The other two DTSs stored concern entirely different systems and are harmless and definitely unrelated.

Strange thing is car is In limp mode and not only we never got a specific code for a transmission issue but now we're not getting the general one P0700 either and it's still in limp.

Basically, we don't have the equipment to dig deeper so it's a guessing game. I'm thinking given all we've tried it's very possible it's a TCM issue, I just have to exclude everything else before I go on buying a new PCM because we can't get it programmed to the VIN here. We can't even quick learn it.

I just needed to hear your thoughts on how you would approach this if you were as unequipped as we are.

So now the questions are the NB! Above and if the next and last possible cause would be the TCM. Please share your considerations on those.

Thank you.

FYI, I dug up the codes from the last read, they're 0013, 0211, 0499 and 0510. Totally off.

Joe,

Sorry for the delay, I was up in the mountains with no internet.

Thank you so much for the schematics! They help explain the system. Needless to say, fuse and relay have been long checked and are good. Our next move will be to open up the transmission and check on the internal connection of the TRS. It will be fun to ping the pins inside and outside too - we will need to have one person probing under the car and another over it. We're planning on it, but I would rather not do it with the car jacked up in the air because it would be tough. I'll let you know as soon as we get it done.

My move now so thanks a lot for all your help so far.

Have a nice day, talk to you soon.

Krassimir

Joe,

The struggle continues. We spent the day checking connectors and harnesses and all is well. We pinged every single wire for resistance at both ends as well as for shorts on all other pins of the harness while looking at the wiring diagrams you sent me. Nothing came out wrong. Transmission is still in limp mode though.

Question:

So now I'm thinking, is there a chance any of the speed sensors could bring back this kind of issue? They go into the TCM too and we have not replaced them. Does it make any sense to go there at all?

Another thing we did is consult our PCM expert here on the phone and the guy said if a signal line was compromised in any way, it would bring back a DTC 100% of the time. So, he suggests we look outside the electrical and electronic components. He thinks it's something that the computer reads as right enough to not bring back a DTC and wrong enough that the car won't run with it. Since the transmission shifts through PRNDL positions fine, the only other thing like that is the fluid. You can refer to my first message with the chronology where we did a service change and the issue disappeared for a while.

I read in a forum that this transmission is extremely whimsical when it comes to the exact ATF +4 fluid.

No other diagnostics available here so we're limited to testing manually.

Basically, please let me know your thoughts on the speed sensors and the fluid as possible causes. Are they even remotely theoretically possible?

Thank you.