94 Buick no overdrive when hot

[another Todd]

94 Buick Park Ave. Ultra with supercharged engine. When ambient temp is high, the car will shift into overdrive for about 20 miles then overdrive will kick out and it will stay in 3rd gear the remainder of the trip. Overdrive will not re-engage until its been shut down long enough for the transmission to cool. Any ideas?

 

[alanu]

Get it scanned. More than likely its thrown a code.

TPS? torque converter? get it scanned.

 

[T-Keith]

Just to verify, we are talking about overdrive, not just the torque converter lock up right? Maybe the coolant temp is getting too high, I don't think they have a trans temp sensor.

 

[another Todd]

Yes overdrive gets locked out, it is not just torque converter lockup. Scanning produces no codes. If the coolant temp is to high would the computer lock out overdrive? I was thinking trans temp sender was bad, but if it doesn't have one then...

 

[dwendt44]

You could put a 180° thermostat in, and change the transmission fluid.
A small transmission cooler would help also.

 

[Trucku]

What does the fluid look like? Is there any indication of the transmission overheating?

 

[Merkava_4]

The overdrive in my Buick will engage right at 45mph when traveling in third gear under no load. For what it's worth.

 

[terminaldegree]

I had this happen to me on a '95 Olds with a 4T60-E also. Very annoying and lasted for a couple of years.

When that transmission finally ate itself [at 130,000 miles -- reaction sun shell broke], there were a few things the rebuild shop did to fix the no overdrive issue: the trans temp sensor was not reading correctly, and the PWM solenoid was replaced. The latter is what seemed to solve the problem.

I know that feeling well: the car just locks itself out of overdrive and into 3rd gear for the rest of the trip. so frustrating...

 

[terminaldegree]

I forgot to add that the transmission proceeded to work beautifully after the rebuild until the car was totalled at 180,000 miles. Hope you can get it fixed.

 

[Gene K]

Ours started doing that. Changed Transmission Fluid and Filter and it stopped. Just a thought if the fluid has been in there a while.