[Oklahoma Wolf]

It's probably dirty connectors. Disconnect the battery and clean 'em all, right up to and including the big one on the TCM itself.

 

[mgill3]

Ah, good call. So, which connectors am I looking for, specifically? Are we talking about the connectors for the sensors?

Thanks for your input.

 

[Bob Lincoln]

The ones to the solenoid pack. Spray them with contact cleaner, clean as best you can and repack with dielectric grease.

 

[Oklahoma Wolf]

Speed sensors, solenoid pack, and TCM. Maybe the range switch, too.

 

[mgill3]

Alright, thanks for your input guys. That helps me out quite a bit. That will be part of my tranny service tomorrow, along with fluid and filter, and a new TCM (if I can find one!)

 

[SGspirit]

This happens to our A604. The symptoms are that it always happens during a drive. It's never in limp mode when we start out.

It happens at irregular intervals ranging from a few days to a couple of months. Usually it happens when coming up to speed after being at a stop, but very rarely it will happen while driving along continuously. Usually there is a little "lurch" that happens just before it malfunctions.

There are never any trouble codes. Stopping and shutting the car off and on again clears the problem. I can do this while driving by shifting into Neutral as long as the situation is very safe and I'm not going too fast.

I've cleaned the main connector on the front of the transmission, with no effect on the problem. The mechanic who rebuilt the transmission has been unable to figure it out.

 

[Oklahoma Wolf]

I should mention that the updated TCM is desensitized to several trouble codes that used to cause limp mode. Might be that's all you need to clear it up. But it's a good idea to clean the connectors anyway. That was the first thing I did for the Imperial when I did the initial ATF+4 flush.

 

[mgill3]

Strange. I'd probably check out every connector and maybe the sensors... sensors could be bad?

This happened to me immediately upon starting the vehicle, and did not go away until I restarted. Also, no codes for me either.

 

[Oklahoma Wolf]

You won't get codes out of the TCM without a compatible scanner. The key dance doesn't work for tranny trouble codes.

 

[valiant67]

Limp mode from the moment the car starts has a good chance of being an electrical/sensor problem.
Limp mode that happens after a lurch is likely because of a low pressure situation. Low pressure causes hard shifting. The revised TCM was more tolerant of low pressure and adapted accordingly resulting in less hard stuffing, bump stops and limp modes.

 

[mgill3]

Well, driving it back home this evening was okay for a little while, then mid-commute it went into limp... shut off in neutral, restarted and it was okay... will be checking everything out tomorrow.

 

[valiant67]

Probably be worth getting it on a scanner that will read the transmission codes so you know what you're dealing with.
Otherwise you could work on all the electrical connectors, get an updated TCM and new ATF+4 in it and still be in the same situation.

 

[SGspirit]

Limp mode from the moment the car starts has a good chance of being an electrical/sensor problem.
Limp mode that happens after a lurch is likely because of a low pressure situation. Low pressure causes hard shifting. The revised TCM was more tolerant of low pressure and adapted accordingly resulting in less hard stuffing, bump stops and limp modes.

Ours shifts very softly. The mechanic who rebuilt it and has checked for this problem is an automatic transmission specialist who is regarded as one of the best in our area. I expect he'd have the right scanner etc. It's just that the malfunction cannot be reproduced on demand, and it's infrequent enough that I can live with it.

Just have to be careful about being in the left lane in heavy traffic when starting up from a stop light on a road that goes to highway speed, because I've gotten stranded in limp mode in the fast lane.

 

[mgill3]

Ok--

After poking around underneath it, my friend found that the plug for the gear selector cable sensor had a broken clip on it, and was also a bit loose... so, I got another plug and butt-connectored it on.

I still was having the same issue after the fix, but I think it may have been the way I was driving the car. I would brake, and then very quickly accelerate without giving the TCM/Trans enough time to finish shifting down before having to shift up again, causing it to throw itself into limp. We have been driving the car and it has been okay so far...

My other car most likely had an updated TCM although I couldn't say for sure (93 New Yorker), so maybe driving this car with the original TCM is just not something I am used to doing. I will continue along and hope for good results, and I'll also clean all the connectors and re-plug just to be sure. I will keep on the lookout for the updated TCM...

 

[mgill3]

Just cleaned the three connectors on the transmission and plugged them back in, all have a rubber gasket around them so i didn't bother with any dielectric (there was none in them)... then, disconnected battery to "forget" everything, and re-trained it....

For the time being everything seems to be very happy and the trans is shifting beautifully, so we'll see how things go!

 

[valiant67]

The symptom you described of having to drive the car a certain way to avoid limp mode is pretty consistent with the issues the upgraded TCM was designed to fix. I suspect you've got a low pressure fluid situation which leads o the slow reaction and the eventual drop into limp mode. Based on your description I don't think the issue is purely electronic. I would get fresh fluid and a revised controller on is as soon as you can. Fresh ATF+4 flows better than old fluid if it's got ATF+3 in it. If it's already got ATF+4 then the problem may be more severe.

You are describing the exact behavior I had with my 1992 New Yorker Salon. But there were times in traffic I could not avoid braking then accelerating without waiting. Eventually I got good at restarting the car while rolling. The ATF+4 fixed the problem of it never going back into limp mode but the shifts were rough and the error codes pointed to a low pressure in some circuit. New updated junkyard TCM and it shifted perfectly afterwards.

 

[mgill3]

Ok, thanks a lot for your input.

I do plan on getting the newer TCM and changing the fluid and filter. I actually found the TCM i need today but i didn't pick it up at the time... it was a bit rusty and i wasn't sure if i wanted that one... if i don't find one by next week I'll be getting that one, removing the cover and grinding it down with a drill and a rust-removal bit, then painting it with some rustoleum... and that'll be okay.

For the time being I'm taking her easy with braking and gassing, etc... it's bee okay for now, but i'll be doing my trans service next week.

 

[Oklahoma Wolf]

I hear you there - my spare updated TCM for the Imperial looks like it came off the bottom of the ocean. Pulled it from a rolled Caravan that had the roof flattened to hood level... it was so rusty that one of the bolts broke off and now has a piece of bolt stuck in one of the mounting holes. Hope I never need it.

 

[mgill3]

Hooray! My friend found me a TCM in perfect condition from Georgia. Rust free, bolts came out real nice, and it was even re-flashed in 1998. My car should be very happy to receive that brain transplant. I'll get that installed some time in the next week or two at the most.

Since I've been driving it nicely, and not gassing it immediately after downshifting like I had been, the car has been working perfectly and without issue.