E38 and AC transducer issue

[bignick]

2011 E38 L96 out of a Chevy 3500 Express van. Came with a fan clutch. I added electric fans. My tuner performed a segment swap with EFI live to get the fans to work.

Fans work fine controlling engine temps.
I have the GM ac transducer installed on the high side ac pressure line.
I have a BP automotive swap harness and their transducer.

I spent this morning tracing wires and back probing connectors to make sure everything was getting the proper signal and voltage. I verified the 5v reference coming in on the gray wire of the ac pressure transducer. I verified 5v coming out of the transducer by jumping the gray wire to the orange & black wire at the switch and back probing wire #12 (orange and black) on the J1 connector at the ECM. So all of the wiring is good. I turned the key on in the truck and verified that the transducer switch was working and I got 1.2V on the orange and black wire.

I can't get the VCM scanner to read anything from the AC pressure transducer switch. I get 0v and 0kpsi all the time.

I'm wondering if I have the wrong segment swap and it's not one that will read the signal coming from the pressure transducer or is this a ECM internal failure.


Anyone have any insight of which segments need to be swapped for this to work correctly? I've found a matching OS in the repository for a vehicle that came with electric fans from the factory.

[bignick]

Got it figured out. And I'll post below what the fix was for anyone else with the issue.

So did some research. Found some of the info on this forum.

So my swap came out of a 2011 3500 express cut away van / box truck.

E38 trucks / van use the ac control head panel to send a message via the canbus to the ecm to control the fans and compressor. Camaros and CTSVs do not. I tried everything I could think of. Segment swap didn't work. I made sure everything was working. Back probed all of the wires in the system. 5v ref from ecm was working. Had a good ground. Jumping the switch sent the voltage back to the ecm. Hptuners, EFI Live and a gm dealership scan tool / laptop would not read any information. No voltage and no pressure.

So I had Geoff at EPS clone my ecm file and wipe another known good E38 ecm and copy my file over. Still the same results.

Went back to my tuner (Justin @ Asylum in Baton Rouge) we had been talking ever since the swap was done back in May about how to get the damn thing to work. I was really loosing hope as he told me he's never gotten one to work. I told him, I'll be the one to figure it out. I'm no tuner, but I'm a damn good troubleshooter. He devoted a morning to troubleshooting and trying to figure it out. He started over with a silverado vin and still nothing. I left him alone and let him do his this.

An idea popped into my head. So I walked into his office and told him about the ac request setup in a Camaro and how it was different from a truck. Asked him if he wouldn't mind pulling a e38 ecm out of another car, plugging it into my truck and we just "key on" the truck and not start it and scan it and see if it reads the AC pressure voltage and pressure .BAM!!!!!!, worked instantly. We had a solution.
So Justin spent some time, finding me a compatible OS for the E38 that would also be compatible with my 6L90e, y'all know. It's all got to work together. Lucky for me I was already using a camaro accelerator pedal, throttle body and maf. So that made it even more compatible with the Camaro OS.

I picked up the ECM last night. Got it home and done! Worked. Sat in my driveway and verified function with HP tuners. Now I can turn my AC on and the transducer will control the electric fans when the ac compressor head pressure creeps up and keeps the relief valve from blowing all my refrigerant out.

So short version:
E38 truck / van OS wouldn't read ac transducer.
Swapped to a camaro OS comparable with my transmission and E38. Now ac transducer functions as it should.
--Side note - the camaro OS requires you use a camaro accelerator pedal.
Shoot me a message if you need any help or have questions.

[LS ROB]

Got it figured out. And I'll post below what the fix was for anyone else with the issue.

So did some research. Found some of the info on this forum.

So my swap came out of a 2011 3500 express cut away van / box truck.

E38 trucks / van use the ac control head panel to send a message via the canbus to the ecm to control the fans and compressor. Camaros and CTSVs do not. I tried everything I could think of. Segment swap didn't work. I made sure everything was working. Back probed all of the wires in the system. 5v ref from ecm was working. Had a good ground. Jumping the switch sent the voltage back to the ecm. Hptuners, EFI Live and a gm dealership scan tool / laptop would not read any information. No voltage and no pressure.

So I had Geoff at EPS clone my ecm file and wipe another known good E38 ecm and copy my file over. Still the same results.

Went back to my tuner (Justin @ Asylum in Baton Rouge) we had been talking ever since the swap was done back in May about how to get the damn thing to work. I was really loosing hope as he told me he's never gotten one to work. I told him, I'll be the one to figure it out. I'm no tuner, but I'm a damn good troubleshooter. He devoted a morning to troubleshooting and trying to figure it out. He started over with a silverado vin and still nothing. I left him alone and let him do his this.

An idea popped into my head. So I walked into his office and told him about the ac request setup in a Camaro and how it was different from a truck. Asked him if he wouldn't mind pulling a e38 ecm out of another car, plugging it into my truck and we just "key on" the truck and not start it and scan it and see if it reads the AC pressure voltage and pressure .BAM!!!!!!, worked instantly. We had a solution.
So Justin spent some time, finding me a compatible OS for the E38 that would also be compatible with my 6L90e, y'all know. It's all got to work together. Lucky for me I was already using a camaro accelerator pedal, throttle body and maf. So that made it even more compatible with the Camaro OS.

I picked up the ECM last night. Got it home and done! Worked. Sat in my driveway and verified function with HP tuners. Now I can turn my AC on and the transducer will control the electric fans when the ac compressor head pressure creeps up and keeps the relief valve from blowing all my refrigerant out.

So short version:
E38 truck / van OS wouldn't read ac transducer.
Swapped to a camaro OS comparable with my transmission and E38. Now ac transducer functions as it should.
--Side note - the camaro OS requires you use a camaro accelerator pedal.
Shoot me a message if you need any help or have questions.

you mentioned it was a swap vehicle; do you happen to have aftermarket ac system or are you using OEM? My swap vehicle uses Vintage Air and i have the trinary switch that controls the fans as well but when the ac kicks on, it almost kills the car if at an idle. i would like to be able to adjust the AC COMPRESSOR table to dampen this but currently not exactly sure how to get the 2 systems to communicate.

[mxcharro]

Hey buy any chance what is the os your tuner used?

[yevgenievich]

Did it take a non canbus ac request signal? I ran in to the same issue on my swap, but I am stuck with truck ecu/os for 4wd low to work