Hi Everyone,

Looking for a bit of help on where to begin in diagnosing a 4L80E / LQ4 Swapped 2005 GMC Sierra. The computer/OBD Diagnostics recognize the truck as a 2006 Silverado 4WD, 4L80E and LQ4. The truck itself is a 2005 GMC Sierra 1500 RCSB. The truck runs and drives well, I don't notice any particular issues at all other than P0103 (I believe the previous owner tuned for Speed Density), and the fact that the Torque Converter never locks up. The lack of Torque Converter lockup is accompanied by P2761 (TCC Pressure Control Solenoid Circuit/Open).

I'd like to get the converter lockup issue resolved, as I have an 823 Headed LQ9 to drop into the truck and will require dyno tuning after. I have an FTI Single Disk 3,200 Converter to go in at that time I do the engine, and would like to make sure all the issues are resolved so that we aren't chasing our tails on the dyno at $200/hr. I have a new solenoid here on the shelf (P/N 24210864) but after doing a lot of reading, I am wondering if this is a wiring issue rather than a hard parts issue. I have access to Snap-On scanners and a hoist, and am wondering if there is anyway on a hoist to confirm the wiring is correct and if the solenoid is being told the right things, prior to actually dropping the pan and swapping the solenoid over.

Any suggestions or tips on checking the wiring? Unfortunately having purchased the truck used, it's tough to know just what was used from the donor truck and what was used from the original truck. I also have no way to contact the previous owner and confirm if it ever worked in the past.

Thanks! Picture of the truck in question and my LS Pull Truck

 

Easiest thing to do is your own resistance check at the 20 pin connector.
Pin E to Pin S

First thing i found with a connector diagram.
Post #1 has the picture.

https://www.performancetrucks.net/fo...g-swap-413157/

 

Unrelated, are those Weld Cheyennes?

 

Ok, so I'm checking for the resistance on the actual solenoid then by checking those pins? I did test the new solenoid and it came back at 10.5ohms, which makes sense as factory spec appears to be 10-15ohms. Assuming it is within resistance range, then we're making the assumption the solenoid should do what it's asked and it instead isn't being told to function?

 

Yes they are, my brother is a Weld Wheel collector. These were sitting in a container so we decided to throw them on when we bought it. They're 20x9 Cheyenne with 275/40R20 Nfera SUR4G tires. Truck is 4/6 Flip Kit with QA1 Single Adjustables up front.

 

Im fixin to find my meter and check a couple 4l80s i have in the shop. But if your reading is good then that means the harness, connector and TCC solenoid is good.
If its bad then well you get to figure out if its the harness connector or solenoid haha.
Easy way to test is to remove that Pin S and put another wire in PIN S, get up to speed and ground that wire. It should lock if everything is good. but with that code you have im guessing you have a wiring issue or a bad solenoid.
Double check PIN S in the connector too. Make sure it hasnt been pushed back into the connector.

 

Perfect. After work I'll get it on the hoist and check the connector, pins and resistance. Kind of hoping it's just a bad solenoid, but getting a feeling it's more than that. Either way, I'll check the basics and see and then report back. Thanks!

 

Just had a look under the truck. A few things I've noticed:

- Previous owner appears to have used a Jumper Harness from the 4L60E Harness to the 4L80E. It is in good condition, and I'm unsure of what to check on that harness if anything.
- Resistance across the TCC Solenoid Pins is 11.1ohms, so right within the normal range. I believe the issue is with the wiring and/or command from the computer.
- ISS is wired and appears to be there, although I have not traced it to confirm if it's wired correctly.

 

Do you have a line pressure gauge to hook up to the test port? It's kind of a pain to get it connected behind the neutral safety switch. ATSG has a spec for what the pressure should be. I'm pretty sure you can manually enabled the TCC solenoid.

Maybe the torque converter o-ring got damaged?

 

The input shaft o ring is very important.
As it seals ATF to be able to apply the lockup clutch.
Ive had lots of issues with those adapter harness's. Ill remove them on every one i work on just to avoid that phone call of a customers truck having issues.

Do you have any tuning software?