trouble code meaning


Asked by Jan 22, 2011 at 05:02 PM about the 1994 Lincoln Town Car

Question type: Maintenance & Repair

I have a 94 town car with that is giving me code 636...transmission oil temp sensor
voltage to high or to low. what could be causing this?

18 Answers

most likely a bad sensor, although it could also be triggered by very old transmission fluid. What the error code really means is that the transmission temperature was out of the specified range during a self test.


The fluid looks very clean. This is a car I just purchased a few days ago with 72k miles. The previous owner supposedly said they never saw a check engine light. The light comes on when a couple minutes after driving and stays on till you cut the car off. It seems to sometimes shift rough going into overdrive and sometimes downshifts rough into 1st if braking hard. Any way to know what sensor or what part could be causing this issue so it can be checked and/or resolved?

1 people found this helpful.

The rough shifting and the trouble code along with the clean fluid are beginning to make me think the previous owner let the fluid go until the point where the car had mechanical problems and after they had the fluid changed the problems persisted prompting them to sell. The problems you describe are consistent with bad fluid, however it is possible that the transmission can still be salvaged. There is a product on the market called auto-rx, personally I have never used it in a transmission (I prefer manual transmissions because of things like this), but I have had great results with it in the engine oil. if you wanna check it out.


Thank you for your advice. There is not a typical senor that trips this code that may need replaced though?

The transmission temp sensor. Try disconnecting it and jumping the connector that plugs onto it with a paperclip. Tape the paperclip in place and take it for a drive, see if it changes the drivability.


In a 16 year old car, you could have a short to ground, short to power, an open, poor connectivity in a multitude of places, etc. I would necessarily condemn the fluid and add snake oil into it to cure your concern. If in fact they had a transmission service performed, the new clean good fluid can cause numerous problems to evolve, i.e. slippage, delayed/rough shifts, etc due to the "slickness" if the fluid. Also, the detergents in new fluid can rejuvenate internal seals causing line pressure issues which in turn will cause drivability problems. Id verify circuit integrity first and foremost then go from there.

I wouldn't call auto-rx snake oil. It's not a chlorinated paraffin. It simply liquefies sludge and grime. As far as a short is concerned, that's what he's going to do to test the sensor. If it were an open, the sensor wouldn't return a code for temp out of specified range. Same for a short. Those would be circuit fault codes. In any event I would start with the sensor since it in an way to reach (albeit vulnerable) location.


I cant seem to locate a trans temp sensor on autozones website. What am I looking for? I am assuming its external if it can be tested with a paperclip. And if a place like Autozone doesnt carry it where can it be purchased if it happens to need replaced?

1 people found this helpful.

It will look like a bolt with a wire attached to a connector in the middle of the bolt head. Most likely this is a dealership only part, so definitely need to isolate it as the problem. Electrical parts have a no return policy (unless you have a friend at the parts counter). If you visit the local dealer they can show you a schematic of its exact location on the transmission.


Thank you. I will check into that. I also got a code for insufficient egr flow which I got on my last town car and seems to be a common problem. On my last tc it was just a matter of changing the egr valve. I will try that first and go from there before tackling the trans sensor. Those are the only two codes I got. The car seems to run smooth engine wise. I bought this car off ebay for 1725 with 72000k so I guess if it needs a couple sensors its worth it. It runs and drives beautiful save for the occcasional rough shift, and even then its so infrequent that you forget its a problem til it does it. I drove it 130 miles home, and have put a tank of gas through it here and it has shifted rough maybe 4 or 5 times, and the engine has never stumbled. I appreciate your help and will update you as I get around to trying different things. With daytime temps in the teens, it may be ahwile. I hope I dont hurt the car. I am not working so it wont be driven to much. To and from VA mainly. Thanks again.


I agree with you! It's not always a bad "sensor" when a code comes up, as some uneducated part slingers would tend to always elude to. As for this "paperclip test", I gotta go back to kindergarden to remember all the fun uses for these things. Unfortunately, this is NOT one of them. Using a paper clip on any 'temperature sensor override test' will produce NOTHING but an error code and make you waste money in the wrong places. Temperature sensors are actually thermistors and work because of resistance. As heat is applied to the sensor, it's inline output resistance will -usually- go down (voltage too high), as it cools the resistance will go up (voltage too low). Applying a piece of metal or paperclip to the end of the sensor plug will do NOTHING but produce a voltage too high code (zero resistance). It is NOT and on/off switch. This will never help you when diagnosing a sensor, as any knowledgeable mechanic would tell you. There is a couple ways to check sensors...the easiest for a 'back yard mechanic' would require the need for an ohmeter and check the resistance of the output prongs at differrent immersion temperatures, but it's an involved process, which requires you getting under a running car, or you can try it on your kitchen stove for a not so accurate result but may let you know if your sensor is at least working somewhat. Towncarlover, if your interested in learning about them let me know and I'll give you a bit of info.

If the test doesn't work for a sensor that measures resistance, than why the hell does it work for an a/c pressure switch? too much pressure = system damage and the compressor will not operate, too little pressure = the same. paperclip it and guess what? IT WORKS.

Resistors have tolerances of +/- 5% and still offer resistance when bad, yes you will have a check engine light on for the circuit fault, but the shifting characteristics of the transmission will not be influenced by the readings of the sensor. You can use heat to test the sensor, however doing it on a stove will ruin it since it wasn't designed for temps above a couple hundred degrees. The other downside to removing it to test is having to drain transmission fluid. Its up to you how big a process you want to make finding out whether the sensor is bad or not.

LETS SEE WHAT THE SERVICE PROCEDURE IS FOR TROUBLESHOOTING? DTCs 56 and 636 Possible causes: o Fluid levels not to specification. o Damaged TFT sensor. o Open harness circuit(s). o Damaged Powertrain Control Module (PCM). * Key off. * Disconnect transmission connector at TFT sensor. Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary. * Insert a jumper wire from the TFT circuit to SIG RTN circuit at transmission vehicle harness connector. <---OMFG JUMPER! * Run Key On Engine Off Self-Test. * Is DTC 66 or 638 present? Note: Disregard any other DTC generated at this time. If no DTCs are generated (module not responding), go to TE12. DAMN DIDNT SAY REMOVE TFT AND PUT IT ON THE STOVETOP. GUESS THATS NOT A SERVICE PROCEDURE, EH?

Here's a pic of the connector to help you


Thank you again. You seem to have some sort of manual. Can you please tell me where on the transmission this sensor is located? And there is no reason to be rude to others trying to help. I do seem to be having the trouble more often now, and it mainly seems to have trouble going into overdrive. If I remember next time I go out I will drive it without overdrive on and see if it still has any issues, though if I get no check engine light or odd shifting, I'm not sure why that sensor would only affect one gear.

1 people found this helpful.

He's a poster who frequently posts on topics I post on in an effort to discredit what I say, and I in turn prove him wrong. Anyways, the sensor is located on the drivers side of the transmission. Its located towards the rear of the transmission, you will have to get underneath the car to access it. Follow he link and enlarge the photo and you will see what I mean.


Thank you very much. I will check into it when I get a chance.

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