1995 GMC Jimmy 4x4 automatic trans, when warm, wont upshift from 2nd to 3rd.?
- Thread starter karen
- Start date
Molson02536
New member
Before guessing at transmission problems, check the fluid level (car warmed up, engine running in Park on level ground) and have the PCM scanned for trouble codes FIRST.
Also note that many problems that show up as transmission issues are actually PCM or electrical, and may be external to the transmission. Secondly, put a line pressure gauge (or visit a local trans shop) on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, trans or pump is worn out. If max pressure is low, check EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.490" boost valve (easy fix in pan).
Shift does not happen at WOT until you let off the gas: Best case: try replacing the TPS. Middle case: leak in the 2nd gear apply circuit (servo assembly or 1-2 accumulator). Double check by using the pressure gauge and watch for a big drop when the PCM commands 2nd gear. Worst case: poor line pressure rise.
Shift is delayed and harsh, may not shift into OD: Check TPS for smooth and linear electrical response over the entire range of motion. If not, replace.
You may have also No 1st or 4th available; trans shifts 2nd to 3rd by itself in D or OD and locks the converter : ShiftA solenoid failed. Easy fix in the pan. Or a wiring problem from PCM to trans.. or PCM.
At worst 1-2 or 2-3 shift is slow/soft above part throttle: Trans is on its way out. Replace or rebuild.
