4l80e

[Yellowfins]

Hello, I’ve been trying to diagnose my tranny with no luck. I’ve got the schematics and other manuals. When I turn my ignition on I have no transmission light at all. I’ve done the jumper wire with no luck either. I do have power at the hot port on the Tcm. Any ideas would be appreciated.
6.5 non turbo
680 miles
Transmission fluid is new
Thanks,
Cory

 

[Mogman]

Welcome to the SS forums!!

 

[AAVP7]

Hello, I’ve been trying to diagnose my tranny with no luck. I’ve got the schematics and other manuals. When I turn my ignition on I have no transmission light at all. I’ve done the jumper wire with no luck either. I do have power at the hot port on the Tcm.

The 4L80 gets power in two ways: There is one permanent 12 volt feed (pin z on Plug J1 at the TCM), and a switched 12 v feed (pin j). This switched feed is only activated by a relay once you switch on vehicle 24 v power at the run-start-switch.

Which pin is the one you call "hot" ?

A pretty common problem with the 4L80 is a sticking 24V/12V relais. If this relay doesn´t close, you won´t get the trans check light. The relay sits behind a sheet metal cover in the RH rear footwell. You can check if the relay is the culprit by removing the plugs 290B/291A and 290C/291C, and connecting both directly. This simulates a closed relay when you switch on run power. If you get a tranny light then, the relay is faulty.