Engine/Transmission (1994 - 1998) Torque Converter Unlocking

[Taz]

What, besides the throttle position sensor (TPS), could be causing the torque converter (tc) to unlock.



I have a new TPS installed. I have also just drove around for an hour with my meeter hooked to the output of the TPS. Even when there is a constant voltage from the TPS, the TC is unlocking. About to go see if I can tap a lead off the TPS sensor lead going into the powertrain control module (PCM) to see if the PCM is seeing the same voltage as is being seen at the sensor.



I'm about to just start pulling connectors, cleaning, and putting in some dielectric grease on them.

 

[JDiepstra]

Unlock when?

 

[Taz]

Unlock when?

Anytime it's locked up. There is no certain speed or throttle position as to cause it to unlock.

 

[RLaJeunesse]

Put you a lock up switch. That will keep your TC locked untill you the switch

 

[fest3er]

Have you checked the fluid level? Low level could cause low pressure, thus not keeping the clutch solidly engaged.

 

[Taz]

Have you checked the fluid level? Low level could cause low pressure, thus not keeping the clutch solidly engaged.

Yes, I have checked all the obvious things. It's definitely electrical in nature.



I am just trying to find out if there is anything else other than the TPS that goes into the logic of the PCM that disengages the TC, i. e. can I isolate this to a single system to diagnose.

 

[Taz]

Put you a lock up switch. That will keep your TC locked untill you the switch

Well yes that is the work around simple solution, but being I have $140 in a brand new TPS I would like for it to work as designed. Never will I buy another automatic anything!

 

[tp0d]

Brake light switch, under the brake pedal. Unplug it and go for another drive. If it is out of adjustment and a bump taps the switch, it will unlock the TC just like cruise control. Might want to double check the truck side TPS connector for any corrosion also.

I would also recommend the lockup switch. I put one on mine, it works great. I didnt mount it in the dash however, I put it on a 36" long tether, with a 3" piece of 1/2" copper pipe, and two caps, with the switch poking out of one end. Fits in the hand well, and is nice and close.

good luck

-j

 

[Taz]

Thanks for that tip. I will check out that switch, it may be the culprit cause that thing sticks a lot.

 

[BarryG]

I second the brake switch. Friend of mine just had the same thing happen and it was a sticking brake switch. At least it is worth checking.

 

[Taz]

Found out the truck will not even lock up the TC with the brake pedal switch disconnected. Something I noticed is that if the switch is disconnected both the p-brake light will stay illuminated and the anti-lock brake light will stay illuminated. Funny thing is about 1 to 2 months ago I had the anti-lock brake light come on then it when off after I cut the truck off and restarted. I may check the wiring diagrams and see if I can short two of the pins on the connector of the brake light to fool the PCM and see what happens.

 

[Taz]

Been so busy I have not got back to report that the problem has been fixed and it was indeed the stop lamp switch! Thanks everyone for that tip! Truck shifts and drives like it is supposed to now.

Now to start working on my car so I can sell it to get a newer truck!

 

[tp0d]

cool, glad to hear ya got it... did you replace the switch or just adjust it?

-j

 

[BHuebner]

Thats good to hear. mine has been doing the same thing and i just replaced the brake switch, but waiting on my seat from the upholstery shop so i can test drive it.

 

[Taz]

cool, glad to hear ya got it... did you replace the switch or just adjust it?



-j

I replaced the switch. All of $15...



To test it though I jumped a wire between pin 3 and 4. That instantly stopped the TC from unlocking and locking.

 

[BHuebner]

The brake switch fixed my problem as well. no more sporadic unlocking. especially from the bumps in the roads.

 

[TSeran]

I replaced the switch. All of $15...



To test it though I jumped a wire between pin 3 and 4. That instantly stopped the TC from unlocking and locking.

Hi,

I know this was posted some time ago, but I was hoping you might answer a few questions:

1. Where did you jump wires 3 and 4? On the brake switch?

2. Where did you find the brake light switch for $15?

3. Would it do any good, or damage, to spray the switch with contact cleaner?

Thanks,

Tony

 

[JonWatson]

i read this thread a couple days ago having this same erratic locking/unlocking problem and i changed my brake light switch and it seems to have cured.



so thanks guys for all the great tips and ideas i was about ot buy a much not needed TPs before i read this thread

-Jon

 

[Taz]

Hi,

I know this was posted some time ago, but I was hoping you might answer a few questions:

1. Where did you jump wires 3 and 4? On the brake switch?

2. Where did you find the brake light switch for $15?

3. Would it do any good, or damage, to spray the switch with contact cleaner?

Thanks,

Tony

1. jumped the wires on the brake switch

2. Advanced auto

3. not as long as you let it dry before you connect power again.

 

[Taz]

i read this thread a couple days ago having this same erratic locking/unlocking problem and i changed my brake light switch and it seems to have cured.



so thanks guys for all the great tips and ideas i was about ot buy a much not needed TPs before i read this thread

-Jon

Glad I could help and you didn't go through my pain!