2001-2005 Chevrolet Silverado CK2500HD C/K3500 GMC Sierra C/K2500HD C/K3500 Allison LCT1000 PRNDL Flash and/or Will Not Move - kw dtc no fifth fourth gear first flash forward overheat GMT800

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

Chevrolet and GMC Light Duty trucks equipped with the Allison LCT1000 automatic transmission may experience: no forward, no reverse, or a will not move, condition. This may be accompanied by a flashing PRNDL display. In addition the vehicle may have any of the following codes stored: P0721, P0731, P0732, P0733, P0734, P0746, P0747, P0776, P0777, P1720, P1721, P1723, P1724, or may have no codes at all.

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If this condition is encountered and you still experience concerns after codes are cleared, disconnect the wiring connection to the transmission. If the condition is still present the C1 clutch may be suspect. Since the C1 clutch is contained within the rotating housing, it is unlikely that there will be very much clutch debris in the bottom of the transmission pan as it will remain trapped within the housing. However, the fluid may have a burnt odor. If this seems like the case, visual inspection and repair of the C1 clutch as per eSI procedures will be necessary.

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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.

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