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Transmission limp mode or nothing?

Tiny
3KR
  • MEMBER
  • 2001 CHEVROLET 2500
  • 6.6L
  • V8
  • TURBO
  • 4WD
  • AUTOMATIC
  • 325,000 MILES
Transmission (Allison 1000) goes into limp mode or nothing. I thoroughly cleaned the valve body, load tested the internal harness and solenoids, checked OHMS, replaced the high-pressure shift valve, no burnt fluid. Codes indicate valve C, D, E, not working. I have been trying to load-test the harness and can't find a wire diagram that matches the harness. At the connector to the transmission position A is a pink wire, (diagram says should be dark green) at the TCM Red connector I have Position 1 pink as well, but my wire diagram from ATSG says it should be blue? Transmission and wires have never been touched by 1 owner. I will attach the diagram I am working from.
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Friday, April 21st, 2023 AT 4:59 AM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
What code numbers are they? Here is a guide to help you test the harness, and the transmission wiring diagrams in the images below.

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

Check the power and grounds to the TCM module, you might have a TCM that is going out. Check out the images (below). Please let us know what happens.
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Friday, April 21st, 2023 AT 4:41 PM
Tiny
3KR
  • MEMBER
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Thanks Ken,

Codes I get are P0763.768.773,1710, they repeat, once cleared, sometimes they stay cleared, and the truck will drive in limp mode, sometimes it takes 2 or 3 attempts to clear them, The number of codes I get changes each time I scan sometimes I get 12 other times 8 or 7 or just 2. Looking at the wire diagram I see pink wire in location1, is that the red connector to the TCM? Tomorrow I will verify the colors by order of the red connector at the TCM. Based on your diagram I need to verify the color and location of the wires, can you verify colors for locations A, B, C, D of the round connector that plugs into the trans (there are 17 wires which matches your diagram), I am confused a little by the letter codes on the diagram.
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Friday, April 21st, 2023 AT 6:42 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
They don't give us the color of the connector, the #2 pin (pink) should have power. It sounds like to me the TCM is out.
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Saturday, April 22nd, 2023 AT 10:47 AM

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