Codes P0740 and P0785, Torque Converter issue?

Tiny
ERINTILLEY
  • MEMBER
  • 1997 GMC SIERRA
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
I went to go start my truck one day and put it in Drive and it fell down into third gear I guess at about 10 miles an hour. So I took it to a mechanic shop and had a rebuilt transmission put in a new torque converter a new ignition switch and a new steering column. When they were done the truck still have the same problem. You start it you put it in Drive start going about 10 miles an hour and it drops down into third gear. The code reader says the problem is in torque converter circuit. It throws a p0740 and p0785 code.
A new powertrain control module was used and I had the same problem. So it's not in the powertrain control module or ECM
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Sunday, January 10th, 2021 AT 6:38 PM

1 Reply

Tiny
KASEKENNY1
  • EXPERT
Unfortunately, this is pointing to an electrical issue so I attached the info below on how to testing this.

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-check-wiring

Please review this material below and let us know what questions you have. Thanks
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Monday, January 11th, 2021 AT 6:34 PM

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