This bulletin is being revised to add Subject information and change the labor operation. This bulletin cancels and supersedes Bulletin Number 03-04-21-006. Please discard Corporate Bulletin Numbers 02-04-21-006D and 03-04-21-006 (Section 04 -- Driveline/Axle).
Some customers may comment that the 4WD/AWD indicator lights on the selector switch do not work, or the 4WD/AWD system may be inoperative and/or the service 4WD light is illuminated. The condition is typically intermittent and always occurs at key-up. Upon investigation, the technician may find DTC C0550 set.
The Transfer Case Control Module (TCCM) has not received the wake-up call during key-up and has remained in the "sleep mode".
When the TCCM is in the "sleep mode", it will not communicate with the class II bus or the Tech 2®.
Important: For the 2002 model year, the TCCM must be replaced and reprogrammed.
For vehicles repaired under warranty, use:
Transfer Case Module - Reprogram with SPS
Some customers may comment that the Service 4WD light is on, the 4WD system is inoperative or the 4WD switch indicator lights are blinking.
Technicians may find DTC C0327 in the Transfer Case Control Module (TCCM). This would indicate an encoder sensor malfunction.
It is also possible that the module may be in a mode that will not allow any shifts or updates for the software or calibrations. If this occurs, the TREC fuse (in the engine compartment) must be pulled and reinstalled after 30 seconds. This should allow further operation and service of the system. If a C0550 code is found, this is an unrelated concern and SI diagnostics should be followed for this concern.
Important: Carefully handle and install the new encoder. Improper installation of the encoder could result in a repeat failure.
Tighten Tighten all four bolts to 13.5 to 17.6 N·m (10 to 13 lb ft).
Actuator Asm (NP4)
Actuator Asm (NP8)
126/226 AB Encoder Sensor
Parts are currently available from GMSPO.
Sensor Assembly, Transfer Case Range Selector - Replace
*This labor time includes reprogramming.
with skid plate