Need Help Please! LS3 swap with 6L80e GMPM CC going in limp mode inconsistently!

[ssresto]

Hello,
I am super struggling with an LS3/ 6l80e connect and cruise swap. I would love and be very grateful for some feedback from all of your experience.

install data-
Ls3 hot cam 500hp
2wd 6l80e converted to a 4wd w/ 3300rpm stall converter I think (higher of the two options from connect and cruise)
no OSS connected initially (speedo has always been correct on vehicle) and nobody at GM could tell me if this mattered
stock trans and engine programming
no tap shift installed, extra tap shift wire plugs included for tap shift are NOT hooked up.


Here is the history of events happening on the break-in tests-

Installed and upon testing almost immediately and at all different times and temperatures the vehicle would start to fail upon restart with no forward gears, only reverse. This happened about 4-5 times. After having lunch and car was cool, after fueling up a hot car, after just reversing and then finding no gears in a hot car, upon cold start... very random. After fidgeting with the shifter, starting, stopping about 5-20 times on average and maybe even doing circles in reverse, it would miraculously find forward gears and I always got it back to the shop.

upon scanning- Found a TCM code of - P0826- "up down shift switch circuit". Cleared it, took the car around the block and the code was back every time I scanned and cleared again.
I would also find an ECM code on rare occasion of P0507 "idle air control system rpm higher than expected"
Made a GM warranty claim and told them I thought it was software issue as it kept coming up with this P0826 code but they sent a new gearbox for swapping unfortunately.

New gearbox installed-
Upon install, I hooked up the OSS just to make sure this was not an issue.... but now we have the below issues.

1st issue- drove about 40 minutes, car cooled completely and upon restart lost all forward gears again and only had reverse. Let it run for 10 minutes to warm up and it was fine, drove home with no issue- no cell - P0826 code in system

2nd issue- Drove about 10 miles and while in 4th gear car would not shift to 5th... let off and it dropped to 2nd and went into limp mode- no cell. got it home at 20mph after a stinky tq slipping experience and after resting the car was fine. P0826 code in system

3rd issue- drove 3 miles and went into limp mode. dash light came on with P0507 code gain. It comes back to my shop tomorrow where I will scan the TCM and I guarantee it will have a P0826 code again.


Here is the kicker-
This is a customer/ friend car and he had me build 2 of them identical, "his and hers". The other just came back from the interior shop and so far has not had ANY of these issues with about 40 miles of testing and lots of stops/starts and does not get a code at all. as a test I did not even hook up the OSS on this one as I am not sure that matters for anything.

I will have both vehicles side by side tomorrow for a few days and I might even try swapping ECU's, do you think this could be an ECU communication issue as the TCM was already switched with a new tranny. The only other thought would be to try a new trans harness.

Is there a tune I need or some programming I am missing? but why would the other work fine? super strange.

I would love to hear any of your thoughts. I want to make this right and certainly stop the bleeding of my time and money on this.

thanks so much
Robb

[TheMechanic]

1. Check powers and grounds. ALL OF THEM
2. Restore any and all stock tune files
3. Verify charging system voltage and possible diodes failed.
4. Ignition OFF, obtain access to the automatic transmission manual shift switch left and right electrical connectors. Refer to Manual Shift Auxiliary Position Switch Replacement - Steering Wheel.
Ignition ON, test for 10–13 volts by backprobing terminal 3 on the manual shift switch-left and ground at the battery negative post.
If less than the specified value, test for a short to ground or an open/high resistance in the ignition voltage circuit. If the circuit tests normal, replace the BCM.
Ignition OFF, disconnect the automatic transmission manual shift switch-right electrical connector.
Ignition ON, test for 10–13 volts at terminal 2 on the manual shift switch-right harness connector and ground at the battery negative post.
If less than the specified value, test the ignition voltage circuit from the automatic transmission manual shift switch-left for a short to ground or an open/high resistance. If the circuit test normal, replace the automatic transmission manual shift switch-left.
Ignition OFF, test for infinite resistance between terminal 1 and terminal 2 on the manual shift switch-right, with the switch open.
If less than the specified value, replace the automatic transmission manual shift switch-right.
Test for less than 5 ohms between terminal 1 and terminal 2 with the plus switch closed on the manual shift switch-right.
If greater than the specified value, replace the automatic transmission manual shift switch-right.
Test for infinite resistance between terminal 2 and terminal 3 on the manual shift switch-right with the switch open.
If less than the specified value, replace the automatic transmission manual shift switch-right.
Test for less than 5 ohms between terminal 2 and terminal 3 with the minus switch closed on the manual shift switch-right.
If greater than the specified value, replace the automatic transmission manual shift switch-right.
Ignition OFF, disconnect the automatic transmission manual shift switch-left electrical connector.
Test for 8.15–8.35 k ohms between terminal 3 and terminal 5 on the manual shift switch-left.
If not within the specified range, replace the automatic transmission manual shift switch-left.
Test for 4.27–4.57 k ohms between terminal 2 and terminal 5 with the plus switch closed on the manual shift switch-left.
If not within the specified range, replace the automatic transmission manual shift switch-left.
Test for 1.485–1.515 k ohms between terminal 2 and terminal 5 with the minus switch closed on the manual shift switch-left.
If not within the specified range, replace the automatic transmission manual shift switch-left.
Test for less than 5 ohms between terminal 1 and terminal 2 with the plus switch closed on manual shift switch-left.
If greater than the specified value, replace the automatic transmission manual shift switch-left.
Test for less than 5 ohms between terminal 2 and terminal 4 with the minus switch closed on the manual shift switch-left.
If greater than the specified value, replace the automatic transmission manual shift switch-left.
Ignition OFF, disconnect the X1 connector at the automatic transmission assembly.
Ignition OFF, connect a 3 A fused jumper wire between terminal 3 and terminal 5 at the automatic transmission manual shift switch-left.
Ignition ON, test for 10–13 volts at the harness connector X1 terminal 7.
If not within the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the TCM.
Repair Instructions

[Alvin]

Hello,
I am super struggling with an LS3/ 6l80e connect and cruise swap. I would love and be very grateful for some feedback from all of your experience.

install data-
Ls3 hot cam 500hp
2wd 6l80e converted to a 4wd w/ 3300rpm stall converter I think (higher of the two options from connect and cruise)
no OSS connected initially (speedo has always been correct on vehicle) and nobody at GM could tell me if this mattered
stock trans and engine programming
no tap shift installed, extra tap shift wire plugs included for tap shift are NOT hooked up.


Here is the history of events happening on the break-in tests-

Installed and upon testing almost immediately and at all different times and temperatures the vehicle would start to fail upon restart with no forward gears, only reverse. This happened about 4-5 times. After having lunch and car was cool, after fueling up a hot car, after just reversing and then finding no gears in a hot car, upon cold start... very random. After fidgeting with the shifter, starting, stopping about 5-20 times on average and maybe even doing circles in reverse, it would miraculously find forward gears and I always got it back to the shop.

upon scanning- Found a TCM code of - P0826- "up down shift switch circuit". Cleared it, took the car around the block and the code was back every time I scanned and cleared again.
I would also find an ECM code on rare occasion of P0507 "idle air control system rpm higher than expected"
Made a GM warranty claim and told them I thought it was software issue as it kept coming up with this P0826 code but they sent a new gearbox for swapping unfortunately.

New gearbox installed-
Upon install, I hooked up the OSS just to make sure this was not an issue.... but now we have the below issues.

1st issue- drove about 40 minutes, car cooled completely and upon restart lost all forward gears again and only had reverse. Let it run for 10 minutes to warm up and it was fine, drove home with no issue- no cell - P0826 code in system

2nd issue- Drove about 10 miles and while in 4th gear car would not shift to 5th... let off and it dropped to 2nd and went into limp mode- no cell. got it home at 20mph after a stinky tq slipping experience and after resting the car was fine. P0826 code in system

3rd issue- drove 3 miles and went into limp mode. dash light came on with P0507 code gain. It comes back to my shop tomorrow where I will scan the TCM and I guarantee it will have a P0826 code again.


Here is the kicker-
This is a customer/ friend car and he had me build 2 of them identical, "his and hers". The other just came back from the interior shop and so far has not had ANY of these issues with about 40 miles of testing and lots of stops/starts and does not get a code at all. as a test I did not even hook up the OSS on this one as I am not sure that matters for anything.

I will have both vehicles side by side tomorrow for a few days and I might even try swapping ECU's, do you think this could be an ECU communication issue as the TCM was already switched with a new tranny. The only other thought would be to try a new trans harness.

Is there a tune I need or some programming I am missing? but why would the other work fine? super strange.

I would love to hear any of your thoughts. I want to make this right and certainly stop the bleeding of my time and money on this.

thanks so much
Robb

I did one of these earlier this week. I think the P0826 is from the tap shift not being hooked up although I could be wrong.

I also experienced this no gear thing.. but it was after a flash. If i turned the key completely off waited a bit and started again it would work.


Good luck. sorry no firm answers.

[relicdew]

P0826 is not going to cause issues. This is a background codes that's set to "no Mil" by default. If it annoys you then go in with HP Tuners and turn that code OFF but it won't cause issues.
If you install an optional tap shifter then the code for P0826 would go away. Sorry I can't help with the other issues though. Hopefully you're 6L80E is from GMPP for their Connect and Cruise and the ECM from GMPP is for this specific 6L80E kit.

I don't know how flexible the GMPP E67 controllers are for the various transmissions but the GM E38 computers must be hardware compatible and have the proper foundation tune to match the transmission.