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97 S10: ignition switch problem..SES light..closed loop

Resolved Question:

I have a 97 S10 Pickup with the code P0785. Fuse # XXXXX was checked and has power all the time so I do not believe it is the ignition switch problem. SES light will come on as soon as closed loop is achieved. Scan tool shows the 3-2 solenoid is commanded on and off. There are no other codes unless fuse 24 is pulled to see the effects, which leads me to believe the trans is receiving power on circuit 1020 otherwise the other solenoids would feed back a code. What do you think?
Submitted: 7 years ago.
Category: Chevy
Expert:  Carhelp4u replied 7 years ago.

I agree with you. If this was a voltage loss type problem, you would be looking at codes such as P0740,P0753,P0758,P0787,P0973,P0976,P1860,P2761,P2764 and/or P2769 in addition to the P0785. There still is a chance that there could be a problem with the solenoid itself, the harness that runs to it, or even a powertrain control module type problem. Testing this problem at this point gets rather difficult and you need a scan tool that can command this solenoid on/off to see if the solenoid is getting the proper voltage and the proper ground to operate. If the solenoid is getting the proper items need to work, but yet is not working, you have a solenoid problem for sure. If the solenoid is missing the voltage side of things, we must really look at this as a possible problem with the internal transmission harness. If you are missing the ground side of this, we really need to first check the resistanct from the negative side of the solenoid to the powertrain control module. If this is found to be ok, you likely have an powertrain control module problem. Here is a wiring schematic of this system so that you can see this solenoid alone.

Object Number: 201197  Size: MF

Feel free to contact me with any questions! Good luck!

Carhelp4u and 3 other Chevy Specialists are ready to help you
Customer: replied 7 years ago.
My scan tool does command the solenoid on and off. I traced the wires at C175 trans connector to see if power and ecm ground on command were there, all is good. Tested trans internal wiring through C175 connector to see if open or shorted to ground, all good. The solenoid itself has only 2.7 ohms resistance, is this OK? I remember most ECM controlled solenoids had over 20 ohms. Could this be the problem? I also noticed the terminals in C175 seemed dark, like corrosion. Cleaned with contact cleaner and connected and disconnected a zillion times. Cleared codes and started up, no light. Roadtested. First time trans went all the way to overdrive and then I slowed at intersection, when started to accel light came on and defaulted to limp-home mode again. Each time cleared code again light would come back as before. Seems like it tried to work but then until it tried to command 3-2 downshift.