Could follow this bulletin. Chevrolet Silverado and GMC Sierra C/K2500HD and C/K3500 trucks equipped with the Allison LCT1000 transmission may experience a condition in which the PRNDL display is inoperative and the Tech 2 scan tool is unable to communicate with the TCM. There may or may not be any transmission performance issues noted with this concern. Trucks equipped with the Allison LCT1000 Automatic Transmission may exhibit any or all of the following conditions:
Unable to communicate with the TCM with the Tech 2
Service Engine Soon light illuminated
Poor transmission performance
Transfer Case Control Module (TCCM) DTCs
Unwanted ABS activation
Circuit 2470 should be checked for an open connection. If C2470 develops an open while the PCM/TCM are powered down, there will not be a code set and the vehicle will exhibit the described symptom. If C2470 develops an open while the PCM/TCM are powered up, it will set a DTC P0700 in the PCM and there will not be any communication with the TCM nor any PRNDL display.
One possibility is C2470 (yellow wire) may be backed out at terminal "R" of the C100 connector, see SI Document ID # 1243943 for clarity. C100 is located in the I/P harness to engine harness, under the fuse block - underhood, see SI Document ID #799333 for clarity. Terminal "R" should be seated and the harness positioned to prevent further strain on the connector.
Other possibilities are:
Ground G110 should be removed, remove frame wax and secured. G110 is located on the left frame rail front cab mounting bracket.
Ground G102 (diesel engine) should be checked for being secure. G102 is located on the lower right side of the engine.
Ground G103 (8.1 gas engine) should be checked for being secure. G103 is located at the left rear of the engine, near the cylinder head.
See if this info works. Post back with what you find.
Thursday, January 24th, 2008 AT 7:34 PM