Transmission issue

1999 CHEVROLET TAHOE
240,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC
Avatar
JASON_PETERSEN
  • MEMBER
  • 1 POST
Okay, my SUV will not up shift or down shift on its own. I can put it in reverse, first, second, and drive just fine with no hesitations and motor runs fine. ECM/PCM has been replaced with new one and has been properly flashed and coded to for vehicle. The motor was replaced by GM 40,000 miles ago, Transmission was replace about 30,000 miles ago. Sending unit and fuel pump was replaced two weeks ago because fuel gauge pegged to full. After replacing fuel pump and sending unit the gauge still is pegged on full. Ignition Module on column has been replaced. Still truck has to be shifted manually through gears and still will not go into overdrive and will not up shift or down shift on its own. Transmission shop that installed it says diagram shows no signal from transmission no damage to wiring harness has been found.
Jun 18, 2017 at 5:52 AM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.
Advertisement
Avatar
HMAC300
  • CAR REPAIR CONTRIBUTOR
  • 48,601 POSTS
you should have a mechanic scan for codes because it can be a broken wire on O2 sensor or anything causing this. the TCM may not be the problem, but you are getting no signal from transmission so there has to be a problem there I would think . it may be a transmission wiring problem like broken inside. i will send a picture along as well. it may be the connector where wiring connects to transmission.
Image (Click to enlarge)
Attached Media
Jun 18, 2017 at 7:37 AM
Advertisement