1G Stuck in 'Limp Mode'

[jrjackso]

i bought a 92 Eagle Talon TSI AWD Turbo Automatic for $100 bucks about a month from my neighbors friend. The guy told me that the car ran fine until one day it just shut down and wouldnt turn back over. So after buying the non running car, I pulled the codes and it turned out that the ECU was junk. So I hunted an ECU down and upon installing it back in the car, I realized that the ECU I bought was for a manual instead of an automatic, but the car fires right up and seems to run pretty good, however the transmission is stuck in 2nd gear regardless and the overdrive dont work. Once I realized that the new ECU was for a manual, I figured that was the problem, so I took the ECU back out and sent it back. From what I have been reading, the transmission problem is not related to the wrong ECU atleast thats what a few people have told me. Apparently there is something called a TCU that controls the shifting in a automatic. So does anyone know whats going on. I have heard about something called limp mode, but I dont know if this a valid problem. Any help would be great and thanks in advance.

 

[jrjackso]

apparently my car is stuck in second gear and from what I have heard either the TCU has went out or the TCU is stuck in limp mode. Does anybody know anything about this problem. Thanks for the info in advance.

 

[luv2rallye]

Yes there is a TCU and it controls shifting. But autos do have a different ECU than manuals (http://www.tmo.com/faq/diagport/970908.htm). For one thing the wiring going to ECU pin 104 is different. It's a ground on a manual but on an auto it goes to the shift selector to tell if your in park/neutral or not park/neutral (which may be part of your problem).

 

[jrjackso]

i really appreciate that. so for now I will just get the right ECU and go from there. I know that there is nothing mechanically wrong with the transmission so I figured it had to be some sort of electrical computer problem. But good looking out. Take care

 

[mkgearhead]

I had a manual trans ECU in my auto Talon and had no problems. I'd try to track down a TCU and go from there. I think the TCU's are all the same for the 1g's, so they should be easy to find.

 

[Doug99RS]

http://dsmtuners.com/forums/showthread.php?t=251126&highlight=TCU

Some of the guys in that thread MIGHT have a bit more information than I do. If it were a 2gnt I could help you more. The only experience I have with a 1g auto was a bad TCU stuck in limp mode which required a whole new TCU. But I've only had experience with one auto 1g problem and wouldn't put all my my eggs in one basket if you know what I mean.
Doug

 

[jrjackso]

got ya. thanks for the info.

 

[94talonwip]

have you had the tranny out for any reason? Your more than likely stuck in 3rd gear. Like the other guys said, a bad tcu can cause that. If you have had your trans out for any reason there are 2 shift solenoid plug ins that are easy to get confused. They are completely interchangeable. When I had the same issue you are describing thats what the problem was. 1 of the solenoids is on the rear of the tranny on the pass. side, and the other is on the front passenger side. Check that if you did remove or replace your trans.

 

[Froyd79]

More often than not if your car is in limp mode, take off the battery for awhile. If it is immediately in limp mode again then chances are the tcu may be a culprit. Or wires backwards etc.

If it is normal and then goes into limp while driving, then it is possibly a bad solenoid or something internally wrong in the trans!

 

[B-Man]

I would check all of the wiring first. I've had lots of problems w/ transmission in my 2g. (which I also have a limp-in thread going). Definatly try a new TCU if you have one available to you.

 

[jrjackso]

as far as I know the car hasnt had the transmission out for any reason. I was actually really suprised that I was having any transmission problems after I replaced the ECU (car didnt run when I bought it) because the car came from a neighbors friend's wife. Nothing was ever mentioned about the transmission sticking, but I cant complain because I bought the car for $100 with the intent to sell after fixing the ECU but then these transmission problems started. I have also did the whole battery thing numerous times and the limp mode was still in effect everytime immediately after. As far as the code checking goes, I have the analog tester, but I am not sure how to check the TCU codes. I think you have to plug the negative into the 12th pin and the positive into either the 6th or 1st pin. I can do that, however and this may sound dumb, but the only way the codes would read is if I had a check engine light on right or is that just to pull engine codes. I have found another TCU that I just paid for so hopefully that will fix the problems, but I would still like to try pulling the code for the TCU just to make sure that this is indeed the problem. Its crazy because the motor the one thing I thought would need some TLC runs perfect and the tranny (never thought would be an issue) is giving me headaches. I just need it running good so that I can sell it because I am moving here shortly and wont have room for it anymore thanks for all the help guys.

 

[B-Man]

http://www.plymouthlaser.com/tcucodes.htm

Here's how to pull codes with an analog multimeter.

 

[freshlane]

It is your transmission speed sensor I believe. same thing happened to my buddy and he replaced it & just like magic everything was good. hope it helps

 

[B-Man]

It is your transmission speed sensor I believe. same thing happened to my buddy and he replaced it & just like magic everything was good. hope it helps

I know on 2g, if the VSS goes out, so does your speedo. But that could be it if it's a 1g

 

[jrjackso]

Well i replaced my TCU because my car was apparently stuck in limp mode. I figured that would fix the problem. Took her for a spin and the car is still stuck in limp mode. FIGURES! Anyways I checked the plymouthlaser.com website for TCU code reading and tried that. Originally there was no codes flashing at all. Then I unplugged the battery for about an hour, hooked it back up and tested the codes again. This time, my analog meter was bouncing consistently at 9 or 10 volts. It seemed to happen relatively quickly, so from what I have read that means the TCU is good. Took the car back out and again, limp mode is still in effect. Parked the car and tested the codes again and nothing. I dont know what all of this means. I have read about transmission solenoids possibly going bad, but my Haynes manual never mentions them, so I have no clue where to even begin looking. WTF?

 

[kyleh]

no CEL ?

 

[jrjackso]

as long as CEL stands for Check Engine Light, there is nothing on which is really strange. I know the light itself works because when the ECU went out, the CEL was on and that went off when I replaced the ECU. So is really strange whats happening I just dont know why sometimes I can pull th TCU code and at other times I cant with a new TCU installed just last night.

 

[jrjackso]

after thinking about this for a few days, i was just wondering if anything else would cause this limp mode issue other than the TCU itself. I mean the new TCU I got could be bad to, the one time I got a code, it scanned back and fourth up to 9 volts consistently. This might sound stupid, but could any timing issues trick this TCU into limp mode. I am just trying to get it out so I can drive the car without the fear of blowing up the engine.

 

[DSMboostin15]

I had the same thing happen with my 92 Laser. Have you opened up the TCU and looked at the board? I had a capacitor leak onto the board and it would cause the TCU to in and out of limp mode due to the acid eating away at the board. I replaced it with a TCU from a junk yard with good capacitors and the problem went away.

 

[jrjackso]

yeah thats what i thought the problem was with the TCU that was in the car originally. so thats what i did. i found one in kentucky and bought it. put it in yesterday and the car was still stuck in limp mode. i didnt know if i had to reset the ECU or TCU manually to make the computer ECU realize that there was a working TCU in there now. if that makes sense anyways before i put the new TCU in, i opened it and inspected the board. there were no obvious blow caps and the board didnt look messed up at all. however, there was a little green dust or film just on the board right behind were the plugs went it. could this be the corrosion?

 

[DSMboostin15]

It kinda sounds like corrosion on the terminals. Try taking a wire brush and cleaning each of the plugs. You may not be making full contact.

 

[jrjackso]

the greenish dust or tint is on the board behind the connectors, so i wouldnt imagine that the connectors themselves are dirty, however i will try at this point. whatever it takes. thanks for the info.....

 

[toybreaker]

Many shops use the snap on mt2500 scanner. It will read codes, and also give a pretty good look at the data stream. If you know a cool mechanic or shop owner, (note, bring beer ) they can plug it in and test drive it to see what's what.

Have them pay special attention to the speed sensors.

I've seen a couple of 1g's with some corrosion and/or heat damage to the harness connectors. They are located in the right front of the car, right above the tranny. Just follow the trans harness back from the tranny and you'll see them.

Good luck, and let us know what you find.

 

[jrjackso]

that will be something to look at. just have to find somebody with this type of scanner so that we can figure out what exactly is going on. thanks for the info. i will be sure to let everybody know how it turns out.

 

[jrjackso]

after realizing you mentioned something about speed sensors, that is the second time that has come up. how exactly do these work. obviously they sense speed but is that information returned to the ECU or TCU. just interested because somebody else has mentioned that the speed sensor could be bad and also a solenoid? my problem is that i have no reference to how transmissions work. WTF