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2007 Chevrolet Express 3500 Duramax
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Discussion Starter · #1 ·
2007 Chevy Express 3500 Duramax (4l85e transmission). Picked up last month for a killer deal but came with transmission problems. Previous owner was not mechanically inclined whatsoever. Stated that the van would not shift out of 2nd gear. I brought it home and scanned it and codes P0787 (Shift/Timing Solenoid Low) P2769 (Torque Converter Clutch Circuit Low) came up. I took it out for a test drive and it would not shift out of 2nd gear. I was able to command the gears using HPTuners and after a while of messing with it I figured out that when I commanded 1st, it was 4th gear, 2nd was 3rd gear, 3rd was 2nd gear and 4th was 1st gear. I was able to drive around like this by commanding the gears except in a backwards order. When I did that the shifts were absolutely perfect.

I then decided to drop the pan, replace all solenoids, the internal wiring harness. Checked the clutch packs and everything, I mean everything checked out. Put it back together and it was the same exact problem, the gears were backwards! At this point I was pretty frustrated. I double checked all connectors on the chassis were in the correct orientation and I even dropped the pan again and double checked that I plugged everything in right. Checked just about the whole chassis wiring harness for any damaged or frayed wires and nothing to be found. Went through every single fuse and none were blown. Went to the TCU and it was replaced 3 months prior by the previous owner and reprogrammed (an attempt on his part to fix the problem).

At this point I am completely stumped. I have checked absolutely everything that I could possibly think of and checked it again…and again. Any help, comments or advice at all would be so much appreciated. Thank you:)
 

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Welcome to DieselPlace
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Welcome to the forum. Have had some intimate time with a 4l80e, and to me sounds like an electrical problem but not sure, maybe someone more knowledgeable will chime in. Good luck!
 

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This sounds similar

 
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Discussion Starter · #5 ·
This sounds similar

yeah i read through that discussion. I believe he was having problems because he did a 4l60/4l80 swap
 

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I believe shift solenoid B is off for 1&2 gear and on for 3&4 gear, while shift solenoid A is off for 2&3 gear and on for 1&4 gear. Ground controlled solenoids. That would be for earlier (pre 2000) 4L80es. If for some reason shift solenoid B was switched (on when expected off and vise versa), that would cause your reversed gears.

If the TCM or the trans itself was swapped and a different year used an opposite shift solenoid B application for some strange reason, that could cause it. But I wouldn't suspect that unless the previous owner had tried to fix it (doing who knows what).
 
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