4l85e backwards gears!! SOS!!
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4l85e backwards gears!! SOS!! 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
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
This may very well just be a HP Tuners glitch/deal. The real question is, do you still have codes? The second gear is stuck in limp mode. It probably has a line pressure issue.
TECH Fanatic
Joined: Jul 2022
Posts: 1,035
Likes: 390
From: Alaska
Put four toggle switches on the dash.
Connect each shift solenoid to one toggle switch.
HomeDepot will set you up with cheap light switches for 99 cents each......
That and 50 feet of 16 gauge speaker wire should get you all fixed up.
Connect each shift solenoid to one toggle switch.
HomeDepot will set you up with cheap light switches for 99 cents each......
That and 50 feet of 16 gauge speaker wire should get you all fixed up.
TECH Resident
Joined: Mar 2012
Posts: 859
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From: Texas
THE FIX IS EVEN CHEAPER!
Teching In
Joined: Sep 2022
Posts: 22
Likes: 2
From: Nigeria-Turkey
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
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
Interesting , a backwards shift pattern would be same as a 4l60e, Could someone have swapped a pcm from a 60e vehical to the truck ? Or be running a 4l60e segment ?
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Joined: Jan 2019
Posts: 677
Likes: 490
From: Roxana, IL
@performabuilt is probably correct!
Along time ago, I had a customer bring me a 98 2500 with a .5.7L 4L80E. he had replaced the intake gaskets and it wouldn't run correctly after that. he replaced wires, cap, rotor, coil & PCM to fix it. After the PCM change, he said it wouldn't shift right. He towed it in and left it for me. I fixed the run problem by setting the base timing to the "0", he had it at 9. Piece of cake, took it for a drive and it wouldn't hardly move, pulled the lever down it got better. down 1 more still better, down again and it slowed up. I said crap this feels backwards as I turned to go back to the shop I saw a PCM in the floor. Sure enough after running the #'s that was for a 2500 truck & a 4L80E. Customer slammed a PCM from a 1500 & a 4L60E.
Along time ago, I had a customer bring me a 98 2500 with a .5.7L 4L80E. he had replaced the intake gaskets and it wouldn't run correctly after that. he replaced wires, cap, rotor, coil & PCM to fix it. After the PCM change, he said it wouldn't shift right. He towed it in and left it for me. I fixed the run problem by setting the base timing to the "0", he had it at 9. Piece of cake, took it for a drive and it wouldn't hardly move, pulled the lever down it got better. down 1 more still better, down again and it slowed up. I said crap this feels backwards as I turned to go back to the shop I saw a PCM in the floor. Sure enough after running the #'s that was for a 2500 truck & a 4L80E. Customer slammed a PCM from a 1500 & a 4L60E.
