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Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC K Sierra - 4WD 🢒 Bulletins 🢒 Repeat TCM Failures with Possible Multiple DTCs - keywords 6.6 8.1 adjust allison engage L18 LB7 lct1000 nsbu P0561 P0562 P0880 P1571 P1760 PQC PRNDL shift slip switch U1000 U2105

Repeat TCM Failures with Possible Multiple DTCs - keywords 6.6 8.1 adjust allison engage L18 LB7 lct1000 nsbu P0561 P0562 P0880 P1571 P1760 PQC PRNDL shift slip switch U1000 U2105

Subject:Repeat TCM Failures with Possible Multiple DTCs

Models:2001-2005 Chevrolet Silverado
2001-2005 GMC Sierra
with LCT1000 (RPO - M74) Transmission


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.

Condition/Concern:

The Allison LCT1000 may experience a condition in which the TCM has repeat failures. Any of the following (but not limited to) DTCs may be set: P0561, P0562, P0880, P1571, P1760, U1000, U1301, U1305, U2105.

Recommendation/Instructions:

Using a DVOM, check the resistance between male terminals 1 and 5 of the C1 connector (grey) at the TCM, with the wiring harness C1 connector removed from the TCM. If this measures to be an open, the TCM must be replaced. The negative battery cables must be checked for being loose.

If the vehicle is experiencing a DTC P0562 and the above check does not reveal the problem, the ignition switch should be replaced.

The following grounds should be checked:

6.6 LB7 Diesel Engine

  1. G104, G105 - Left Battery Ground
  2. G102 - Right Battery Ground

8.1 L18 Gas Engine

  1. G100, G105 - Left Battery Ground
  2. G106 - Right Battery Ground with 8Y9 or TP2

The Master Electrical Component List in SI provides Ground location information.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.