| Subject: | Information on Noise and Bump/Clunk Felt When Transfer Case Shifted into Four Low (4LO) -- Normal Four Wheel Drive Shifting Characteristic |
| Models: | 2004-2008 Chevrolet Colorado |
| with Electric Shift Selectable Transfer Case (RPO NP1) |
This bulletin is being revised to add the 2008 model year. Please discard Corporate Bulletin Number 04-04-21-002B (Section 04 -- Driveline/Axle).
Some customers may comment on a grind noise or a bump/clunk felt when shifting the transfer case into 4LO.
| • | The grind/bump/clunk felt when the transfer case electrically shifts into 4LO is due to the engagement sequence that applies engine torque through the transfer case, front differential and front axles. |
| • | The noise, present in all electronically shifted 4WD systems, is considered normal operation and does not pose any potential to impart damage by shifting into 4LO. |
| • | The noise level in the Colorado and Canyon is louder than in larger vehicles due to the vehicle size and transfer case design. |
| • | The noise level can be reduced by following the Owners Manual Instruction of shifting while in neutral and in forward motion of about 4 km/h (3 mph). |
| • | Alternatively, the noise can be eliminated by shifting into 4LO while in a key on engine off condition. |
| • | DO NOT REPLACE the transfer case in an attempt to repair this condition. |
| • | DO NOT attempt to make repairs to the transfer case at this time for this condition. |
| • | DO NOT attempt to reprogram the transfer case control module (TCCM). The TCCM is NOT REPROGRAMMABLE on this vehicle. |
| • | DO NOT replace the TCCM in an attempt to repair this condition. |
| • | DO NOT replace the transfer case actuator in an attempt to repair this condition. |
| • | General Motors encourages dealers to share this information with concerned customers. |
