JTail

I have a 2001 Suburban Z71 that won't shift into overdrive. It shifts thru the first 3 gears but not into overdrive. What could possibly be happening?

golfer

Could be the torque convertor lock solenoid which engages for overdrive.

JTail

thanks, I'll check it out!

engine2

How many miles on the tranny?

ZX1100F1

Usually when a no 3-4 shift occurs it is a faulty accumulator or servo, on occasion a stuck valve or bad pump can also cause the problem.
In any case it is not a home repair, however I always recommend the fluid and filter be changed before taking it in, it is cheap and sometimes solves the problem.

JTail

90,000 miles on the tranny... overdrive is working again... go figure!!! the Service Engine light went out... dealership "cannot duplicate problem". Kinda reminds me of going to the dentist with a toothache.