My sons 1994 Regal possibly is starting to have a problem with the transmission. It shifts fine through all of the gears but once in OD, I can see the RPMs raise when you give it just a little gas and then in just a little bit the rpms drop and you hear it has shifted back to od. This only happens if you let off the throttle, let the car coast, and then press the throttle back down again. you only have to press the throttle just a little for it to kick out of OD.. If you are on a flat and in OD and do not let off the throttle by just feathering it so tat it is not quite coasting, you can press the throttle way down and pick up speed without it downshifting out of OD. Of course if you press it too far down it will downshift like it should. So it only seems to happen after coasting and then giving it the gas again. IT can be say just enough throttle to pick up 2 or 3 miles per hour while on a flat or pickup what you lost coasting. And the coasting can be just letting off the gas peddle for a second or two and then right back down.

I cant quite tell if the transmission is slipping or not because it shifts so smooth. I don't believe it is though because watching the RPM gauge when it down shifts, it goes from say 1500 to 2500 and if i press the gas peddle like I'm trying to pick up speed, the car does pick up speed normally.

Will it hurt for my son to drive it in 3rd around town? The highest speed limit from home to his work in town is 45mph and that'* only for a mile or so.

Should he be driving with it in OD around town anyway? The shifter shows a D instead of OD. I have a 88 Ford van with a AOD transmission which has D and OD. it was always recommended to drive in D unless on the highway or long stretches so it wouldn't be shifting back and forth between D and OD.

Thanks in advance and any advice would be more then welcome..

Oh the last time we were working on the car I bought the Actron CP9145 scanner. Will it read transmission codes also? IF I remember correctly, this 94 regal is the in between OBD1 and OBD2.....

I believe this to be completely normal. TCC will unlock when it sees 0 TPS, and will engage only when TPS is between a certain TPS range and certain engine load.

3rd gear is fine for tootling around town.

If and any trans codes are stored in the ECU which the CP9145 should see.

Mike is dead on, when throttle drops to 0%, the TCC unlocks, and will lock up again once proper criteria is met.

And, in all honesty, it will not even shift in to 4th below 48mph any way, and lock the TCC in 4th below 50mph. Your case sounds perfectly normal. It will lock the TCC in 3rd at 36-48mph, which is probably the exact range the vehicle is being operated in.

You can confirm the TCC is unlocking by holding steady throttle at the speeds you are noticing the issue at, and with your left foot, start to slightly ease on the brakes. As soon as you start to get on the brakes, the TCC should unlock, and should reengage within a couple of seconds of releasing the brake pedal. You will see engine speed rise, then settle back down.

And, as Mike said, transmission codes show up as Pxxxx codes, and should pull with the CP9145. If there'* no codes, I wouldn't worry about it. It sounds like everything is working exactly as it should.

Make that three.

Make that four, plus: I've heard a couple of reasons for this:

- If you are about to lock the brakes up, the converter clutch is unlocked so as to not stall the engine. If you were about to be in that situation, you'd theoretically lift off the gas pedal first
- If you lift off the gas, the converter clutch disengages and this allows the engine speed to drop a little, allowing the car to coast a little more freely, saving some fuel in the process.

They started doing this when the first locking converters hit the market back in the `80s. Many of those were rear-drive therefore more prone to locking the drive wheels.

I bet one was intentional and the other was bonus. Either way, sounds like yours is working just fine.

Thanks guys! One more question about this though. Mike and Rjoly87 said when TPS is 0.

My son is out of town in the car right now so I can not test drive it. If I remember correctly though, and I may be wrong, I didn't always let off of the accelerator enough for it to come all the way back to the idle position. Only the idle position would be 0, correct?
He drove the car in 3rd on his 100 mile one way trip and when I talked to him he told me that it did fine.
I will drive the car again and double check the position of the throttle when the it happens.


BTW thanks again to all that helped my son and I when we had the cylinder heads off. That was almost 10,000 miles ago and the car is still running! All we have done since is the normal oil changes and flushed the water out and added coolant.

Thanks Again
Anna

When we say TPS 0, we are referencing when the engine computer sees zero input from the Throttle Position Sensor which is located on the throttle body. In English, this means foot completely off the gas pedal. Push the gas pedal halfway down, the engine computer will see about 50% TPS.

Thanks Mike! So, say the computer sees 3 volts from the TPS while driving at a speed of 60mph. As you said when I let off the gas peddle all the way, the computer will see 0 volts and the TCC will unlock.
What if I am going 60mph and only let off of the gas peddle for a second or two but not all the way, but the computer sees a drop in voltage from the TPS. Lets say from 3 volts to 1.5 volts and right back to 3 volts. Will the TCC unlock during this condition?

I will be able to test drive the car this afternoon or tomorrow. What I remember was: Say the gas peddle is 1/2 way down to go 60mph and i let off of the peddle only a 1/4 of the way and then press it back down again, the transmission will downshift for a short time and then go back to overdrive. During this condition the computer did not see 0 volts from the TCC.

If I let off of the gas peddle, just to where the engine is not pulling at all and feather it as the speed of the car slows down, the transmission will stay in OD This I understand is normal unless the speed drops below 48 or is under a load meeting certain conditions.

Sorry if this is redundant.
Thanks
Anna

It really depends on what the software is looking for. There are so many factors that contribute to a TCC unlocking/locking, its very difficult to narrow it down. A misfire will cause it to stay unlocked, engine temp below a certain temp will keep it from locking, trans temp will keep it from locking, the list goes on.

TCC will lock when load is steady. Give it throttle and it unlocks. Once steady again it will lock again. Throttle opening, engine speed and load are the determining factors to TCC. That, and the correct gear select.