4l60e need help

[Thousanddollerchevy]

I have a 1993 c2500 with a 350 and a 4l60e. I am getting a code 66 and my transmission will start in 3rd unless manualy put into 2nd and no 1st or 4th gear. I have changed all the transmission solenoids, the transmission wiring harness, and transmission filter. I have checked for power on transmission wiring plug on pin e, which is what I researched to be the power imput to the transmission and got nothing key on engine off. the fuse that said trans tested good, so I also replaced the ignition starter switch. But nothing has solved the issue ? Any help is appreciated thanks

 

[Schurkey]

1--2 shift solenoid, or the wire harness for the 1--2 solenoid all the way back to the ECM would be my first guesses. Potentially, the ECM circuitry for the 1--2 solenoid could be burnt-up.

Despite the name, the 1--2 solenoid is only "on" in 1st and 4th gear. If the SAE weren't so meddlesome, and if GM had more sense, they'd call it the 1--4 shift solenoid.

 

[GMTMark]

Code 66 shows to be low or high pressure in the AC system so that should be unrelated to that issue in your transmission. I think you might have a harness problem. Check the big connection going into the tranny and make sure it is lined up and connected well. It could also be a problem in the PCM. Do you have AC? Has it been worked on lately? Could be a defective pressure switch.

 

[618 Syndicate]

Can you measure voltage at the trans fuse and verify it's a full 12? Evidently the ignition switch can have issues and cause low voltage (6-8v) to the trans through that fuse.
I had very similar symptoms about a month ago in a NBS truck and that advice was given to me. After pulling a replacement trans but not installing it, dropping the pan and replacing all the shift solenoids, it turned out that fuse was blown, replaced it and haven't had an issue. I had added power for helper bags through that fuse (marked IGN-0 on newer trucks) and had a short in the wire causing the fuse to blow.
It's far more likely that you have an electrical issue than all your shift solenoids going bad at exactly the same time.

 

[Sabinoerc]

I have a 1993 c2500 with a 350 and a 4l60e. I am getting a code 66 and my transmission will start in 3rd unless manualy put into 2nd and no 1st or 4th gear. I have changed all the transmission solenoids, the transmission wiring harness, and transmission filter. I have checked for power on transmission wiring plug on pin e, which is what I researched to be the power imput to the transmission and got nothing key on engine off. the fuse that said trans tested good, so I also replaced the ignition starter switch. But nothing has solved the issue ? Any help is appreciated thanks

My 93 has a membrane switch in the trans which went bad once and caused OD to stop working. You have different symptoms but sounds like you were replacing everything - did you replace that membrane switch?