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M
4L80E won't shift out of 1st

Thanks for the reply. No codes to be had though. No comms with the ECM either with a scan tool or paper clip. I thought of TPS also. That could effect the idle issue and the trans needs to know throttle position. I tried one (although I admit it was a cheap aftermarket one), no change...
- MarylandMike
- Post #10
- Jul 17, 2022
- Forum: Transmissions
M
4L80E won't shift out of 1st

Wondering if you had an update. Any trouble after this? I'm having a very similar problem with my 93 K2500. No comms with the ECM and same trans issues. If I disconnect the ECM for a while, it will run and shift perfectly for a drive cycle or two. Then, extended crank, finally starts and...
- MarylandMike
- Post #8
- Jul 16, 2022
- Forum: Transmissions