OT: Any GM transmission experts out there?
 

Got up this AM (first cold day of the year) and drove to work in My GMC Jimmy (4.3L, 4WD, Auto, 92K mi.) and the transmission wouldn't go into overdrive (4th gear). Just stayed in 3rd. No slipping or unusual shifting, TCC seemed to work. It just wouldn't go into OD.
Stopped, checked fluid level, it was 1/2 qt low, a little dark, but didn't smell burned. Topped it up, now it shifts fine into 4th. Asolutely normal.
Is that normal? Or is my tranny going bad?
Gary

Stuck accumulator or servo.

I'm no expert, but I've been told that they have electronic sensors in there that go bad. I know a guy that had his shift into second, and it stayed in second gear due to some sensor in there...

But, we all hope that all you need is a good trans fluid change/flush...:)

That 1/2 quart low can make a difference. Especially when it's cold, the fluid doesn't expand as much.

I also recommend a fluid service. Heat kills fluid and it sounds like yours has been slightly toasted.

May be temp sender to ecm, no closed loop no overdrive. till it reaches correct temp

Worked fine today> Going in for a fluid change this weekend.
BTW scoobie, I think you get overdrive at under 100 degrees, or with a faulty sensor, you just dont get TCC lockup.
Gary