Transmission stuck in 3rd

[mattd1979]

I have 3 codes on the trans diag display on the dash which are 1,2, and 3. The first two are for turbine sensor and speed sensor. The 3rd one is for the throttle position sensor. I was headed home and the car was doing fine. I missed my turn and backed up and then put it in 1st and when I was making the turn onto the street, the tires were cherping a little and then the car went straight into 3rd while the shifter was still in 1st. When I came to a stop and accelerated, it started in 3rd. So when I got home, I performed the above diagnostic and got those 3 codes. What could cause all 3 of the above codes to pop up at once? Has anybody else had this problem before? I checked all of the fuses under the dash and under the hood and all are good. I looked under the car but didn't see any wires hanging loose. I was supposed to be leaving for Jacksonville tomorrow which is a 3 hour drive.

[Rex]

Sounds like it's gone into "fail safe mode", search on that phrase.

How's your battery? (sometimes causes trans weirdnessDo you have a spare TCU?Do you hear any funny sounds (clicking)?

[elwesso]

did turning the car off for a minute help? how about unplugging the battery?

[mattd1979]

I decided to test the 3rd sensor that was listed first because it didn't involve driving the car while trying to hold the test probes to the connectors in the TCU. It tested fine. I then decided to drive the car to a straight road with little traffic and noticed that it was shifting again. I drove it up to 60MPH and then would come to a complete stop and repeat. Each time it shifted thru all of the gears. I did notice that it seemed to have a slight delay going into 4th during a light accel up to speed. When I drove it back home, I performed the on-board test again and this time I got an "OK". As far as the battery, it starts up without any drag like its fully charged.

[MinisterofDOOM]

I had a similar issue where the TCU would intermittently fail leaving the car with only 3rd gear. Anytime I was not applying constant throttle, I could feel the trans "pulsing" as though it was shifting back and forth from neutral to 3rd.My car would also sometimes run perfectly normally, with self-diagnostic returning an "OK". There was a weeks-long duration wherein the car ran fine, then the problem came back. Other times it would be totally random, sometimes going from working fine to 3rd-only or the other way around spontaneously while driving.

As Rex noted, if you have access to a spare TCU, it would be a good diagnostic tool. My cause ended up being a faulty TCU, replacing it cured the problem for good. I only discovered the real cause, though, after several diagnoses looking for and replacing supposedly bad sensors, etc. If I had to do it over again knowing what I do now, I'd want to start by testing with a known good TCU. If that doesn't solve it, THEN I'd move on to testing individual sensors.Another option is to have a dealer connect a consult and run a basic diagnostic. This must be done WHILE the car is malfunctioning. DO NOT turn the car off when you take it to the dealer. Leave it running. If you turn it off and the car starts functioning correctly again when they start it back up (this happened to me more than once) the Consult won't see anything wrong. It has to be malfuctioning WHEN tested for the Consult to be able to tell if there's a TCU issue (mine showed as not communicating with the ECU in the diagnostic results).

The 3 codes you list are the same codes my car's self diagnostic was returning when broken. It also returned "AT CHECK" which I initially thought was related to the TPS error code, but in the end turned out to mean the TCU was bad (the AT CHECK error can indicate any one of a few things, as the FSM shows).

Whatever you do, don't let the dealer talk you into throwing parts at the car until you've ruled out the TCU possibility. With fairly plentiful sources for used TCUs, it's a cheaper cheaper and easier repair. That way you won't end up replacing more costly parts unless it's necessary. For instance, I replaced the TPS, and both "3" and "AT CHECK" continued appearing in AT diagnostic results, proving that the TPS error code was an error in itself.

[Q45tech]

Concur , always swap in a known good TCU. Sometimes the connector to TCU will develop a contact intermitent from age abd corrosion----------spray contact cleaner.Also check connectors at transmission for similiar problems.