[ImperialCrown]

Welcome to Allpar. There are 2 coolant sensors, one single wire one for the dash gauge and one 2-wire one for the PCM. The 2-wire one is the one that will throw a PCM fault code.
The TCM stores transaxle fault codes and needs a special code reader to access those codes, if it comes to that. Engine coolant temp could possibly put the transaxle into limp-in as the 1989 valve body may not have had an internal ATF temp sensor yet.

 

[vcbutton]

Thanks. Here's a couple more symptom: Temperature is reaching 190 Degrees +-. Temp gauge is barely off the peg. After resetting the codes (by disconnecting battery) I'm still locked in 2nd gear but no fault code! I there a way to reset the transaxle fault codes?

 

[ImperialCrown]

A battery disconnect will also reset the TCM (transaxle control module) fault codes, but if it returns to 'limp-in' immediately afterwards, then you have an active or 'hard' fault code that isn't going away. If it is going into 'limp-in' (2nd gear), then the TCM has a fault code(s) stored in it.
There may be a problem with the single (violet) wire temp sensor if the temp gauge isn't being accurate.
How are you reading fault codes? The 'key dance' and counting the engine light blinks will only show you engine (PCM) faults and not transaxle (TCM) faults. You will need a special OBD 1 scan tool with the specific Chrysler connector cable to read TCM codes (like the DRB II or DRB III with Supercard or equivalent). The TCM communicates through the body diagnostic connector in the vicinity of the interior fuse box.
http://jeep.zerok.ru/images/ATD-AW4/3.gif

 

[vcbutton]

Thanks for the great info. You're right, I'm doing the key dance. I'll have to find someone with a special scanner. Surely, there must be a simple way to reset the code in the TCM!

 

[Bob Lincoln]

Thermostat stuck open is usually the cause of a code 17, and that would keep it cold and in open-loop mode. Draining the system may have aggravated an aging thermostat. I'd replace it and make sure the air is bled out afterward.

 

[valiant67]

Surely, there must be a simple way to reset the code in the TCM!

Disconnecting the battery does that (at least with the original computer, replacement computers have permanent memory that is not reset).
Assuming the battery disconnect resets the computer but the transmission still remains in limp mode, the fault is a hard code as mentioned above. Some codes will immediately put the transmission into limp mode, others only after they occur a certain number of times during car operation. You really need the diagnostic codes from the transmission to diagnose it.

 

[vcbutton]

Thanks for all your help. I'll be looking for some local assistance.

Not solved, but progressing.

 

[vcbutton]

I have information that according to the service manual, there is NO TCM on this vehicle. The only readouts are from the ECM (or PCM). This controls the solenoid block on the transmission. I don't know who to believe! Very frustrating!

 

[Oklahoma Wolf]

New Yorker Landau? There's a TCM. It's on the inside fender, passenger side, behind the headlights.

 

[ImperialCrown]

Wrong or misleading service manual. The PCM and TCM weren't incorporated into the same housing yet.

 

[valiant67]

1988 would not have a TCM (as it used the old 3 speed auto which did not need one and had no solenoid pack).
But the posters above are correct, there will be one there for 1989 in the New Yorker.

 

[vcbutton]

I found someone who has a Snap-on diagnostic tool that can read the tcm codes. I have a code 41. (That's the low/reverse solenoid circuit) Following the troubleshooting flowchart, I have conclude that I need to replace the controller. I can't find a part number on it. Can someone look that up for me or refer me to a site where I can? Thanks

 

[Oklahoma Wolf]

Look for 4796121 if buying a used one. Newest part number at a dealer would be R4761846AA.

 

[vcbutton]

Good news! purchased TCM (P/N4557120) on EBay, for about $30. !5 minutes to replace and problem solved. HooRay! Now if I can get the rear airbags to inflate ...

Thanks everyone, for your help.

 

[Oklahoma Wolf]

They're probably leaky. Assuming the compressor works, Slime tire sealant is probably the only option open unless you can find some NOS air shocks on eBay. These are no longer available at the dealer.

If the compressor's also gone, you might as well convert to either Dynasty rear shocks and springs or aftermarket air shocks.