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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1685
Experience:  GM Grand Master Technician 2007. 14 year experience.
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I am getting P0740, P0785 And P0001 after initially changing

Customer Question

I am getting P0740, P0785 And P0001 after initially changing out the inocente sensors due to getting coses for both of them. I also changed out both shift solenoids due to the transmission not shifting properly. Now I'm still not shifting properly And I'm getting the DTC's mentioned above.
Submitted: 1 year ago.
Category: GMC
Expert:  Gary replied 1 year ago.

I am sorry your having this problem

as soon as you clear the codes they come right back ?

do you have a multi meter on hand ?

Customer: replied 1 year ago.
Expert:  Gary replied 1 year ago.

can you idle the truck and see if the fuse called IGN0 in the drivers side inside fuse box shows 12 volts at both sides of that fuse testing it in place through the little openings in the tops of that fuse ?

Customer: replied 1 year ago.
I have 14 volts across the fuse. I've also checked resistance across the solenoids and they are both reading 20 ohms each. I've checked that the wires are in the correct location and that they have good continuity. I am also getting 12 volts to the transmission. The knock sensor code is now gone but the other codes mentioned before are still active. The engine also likes to idle high, around 3-4k if I burp the throttle and then will settle down after about 20 seconds. I am now noticing an oil leak on the transmission and it apears to be coming from the oil pump. As this is a newly remanufactured transmission, I doubt that it is the input seal but maybe the oil pump is lose and leaking there. When I dropped the oil pan from the transmission, I found fine black metal particles along with a few very tiny pieses of metal slivers in it. The engine and transmission have just been remanufactured and it is a swap from the original 5.3/4L60E to a 6.0/4L80E. The harnes has been rewired by professionals and the ECU has been reflashed by their engine builder. The original engine and transmission worked fine before the swap but I wanted more than it could give me. Lol! Now I have a bigger headache then I barganed for!
Expert:  Gary replied 1 year ago.

do you have any access to a scan tool that has functions on the scan tool to command on and off the shift solenoids and tcc solenoid ?

and to be clear this has a 4L80 in it now ? and this swap used to have no codes or check engine light and shift fine after the swap ?

Customer: replied 1 year ago.
No I do not have any access to a scanner with those functions. This swap has never worked properly. The check engine light comes on every time that I put the truck in gear and the transmission goes straight into what seems to be 2nd or 3rd gear and then at 7MPH the torque converter locks up and almost stalls the engine.
Expert:  Gary replied 1 year ago.

did this engine and transmission swap ever shift correctly and NOT have any codes ?

Customer: replied 1 year ago.
You are wasting my responses and don't you don't have a clue so you are asking me the same questions over and over again even though I have answered them already. I will not be paying for this service and I knew that you couldn't figure out my problem. Thanks for the waste of time.
Expert:  Gary replied 1 year ago.

which computer are you using with this swap ? the one from the swap or the original one ?

we also need to see if the TCC and the 3-2 shift solenoid is being activated with a scan tool turning them on and off and see if the ground signal is present at the connector at the transmission

with both those codes and 12 volts at the pink transmission wire we are either not getting the 12 volts in the internal wiring harness to the solenoids or the computer is not sending the ground to turn on either the tcc or the 3-2 shift solenoid but from the sounds of this since the transmission seems to go into lock up there is a chance those ground signal wires are shorting to ground causing this lock up at 7 MPH

i have a clue thank you when you have a transplant like this there is NO exact flow chart to find this problem we have to make sure on a lot of things

like : which computer are you using

: can we command on and off the tcc and the 3-2 solenoid ?

is the computer grounding the correct wires for this swap over ?