6l80 connect and cruise intermittent no forward gears.

[levi1a]

Dug through the forums and found a user with exact issue. No resolution posted. Did reach out in PM so hope to hear back. GM performace LS3 connect and cruise package. Transmission randomly has no forward gears at first startup in the morning. Can disconnect and reconnect the bulkhead connector for the trans, and transmission immediately functions normally. GM performance techs havent been much help. Want to replace the Trans as unit due to the connect and cruise diag cable being married to the TCM and the cable is no longer available. Any one else with this issue or can lend some insight. Prior to unplugging I did verify trans is showing commanded state for gear section.

[relicdew]

When this happens, are you able to plug in a scan tool and see if any codes are populating?

[levi1a]

Yes has a P0826 tap shift code, but tap shift is not connected so assume it is a generic code. Also not setting a hard fault code as check engine light is not on. Code is present when trans is functioning normally as well.

[Alvin]

Have you modified the TCM file in it with HPtuners? You are not technically supposed to. after a flash it will do this.

[levi1a]

No changes to the TCM. We did change the on off temps for the electric fans but had the same issue once before.

[TransGo Robert]

Without a log it's always just a guessing game, but you might be dealing with the usual wrong our checkball number 1 causing intermittent no forward engagement.

[Alvin]

No changes to the TCM. We did change the on off temps for the electric fans but had the same issue once before.

Did you accidentally flash the TCM? It will by default if you've read both. Just flashing it will cause this. Not necessarily making a change.