Torque Converter & Dash Issues, + P0740 and P0785 Codes

[TStowell]

Hi so ive got a 1996 C1500 with a L31 and 4L60E and suddenly while driving i lost power I could feel it was something wrong with the torque converter because in park i revved great no bogging. In drive it normally only drops down to around 1000 RPMs like it should but it now it would try to sit below there . I limped the truck home and found that I had a P0785 Shifting Timing Solenoid A code and a P0740 Torque Converter Clutch Circuit Open. Also a couple days before I started experiencing issues with my dash it started acting funny suddenly my speedometer would fly around and on the dash my tach would read zero or jump around I plugged in my Autocal Scanner and data logged and looked back my VSS were reading normall and my rpms stayed steady and where they should be so its definitely a gauge problem. Im looking for stuff to check first I recently did a 0411 Swap and it had been running great for about a month before this so i will check wiring and the actual PCM first. (The fact that its 2 codes at once and dash problems makes me think a wiring or PCM issue). Any other recommendations are greatly appreciated.

 

[NickTransmissions]

Hi so ive got a 1996 C1500 with a L31 and 4L60E and suddenly while driving i lost power I could feel it was something wrong with the torque converter because in park i revved great no bogging. In drive it normally only drops down to around 1000 RPMs like it should but it now it would try to sit below there . I limped the truck home and found that I had a P0785 Shifting Timing Solenoid A code and a P0740 Torque Converter Clutch Circuit Open. Also a couple days before I started experiencing issues with my dash it started acting funny suddenly my speedometer would fly around and on the dash my tach would read zero or jump around I plugged in my Autocal Scanner and data logged and looked back my VSS were reading normall and my rpms stayed steady and where they should be so its definitely a gauge problem. Im looking for stuff to check first I recently did a 0411 Swap and it had been running great for about a month before this so i will check wiring and the actual PCM first. (The fact that its 2 codes at once and dash problems makes me think a wiring or PCM issue). Any other recommendations are greatly appreciated.

Do the checks you suggested above then report back. Once you have eliminated wiring (or at least let us know you have done so), we can perhaps make more suggestions.

It's not entirely unheard of for two solenoids to go bad at the same time, though admittedly it's relatively rare but you may want to continuity test the transmission's wiring harness via the pins on the harness case connector. Also check the connector on the vehicle wiring harness as well just to rule it out as a potential source of your problems. Id then drop the pan to test the 3-2 control solenoid. That solenoid should show 18-24 ohms, same with the two shift solenoids...The EPC shows 4-6 ohms while the PWM solenoids is 9-12 ohms.

P0785 indicates a problem with your 3-2 control solenoid.