Misfire Bump Or Multiple Bumps After A 1-2 Upshift - keywords AWD buck chuggle shift shudder surge

This PI was superseded to update models. Please discard PIP3154B.

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

The condition can be perceived as an engine misfire, surge or bump typically during or just after the 1-2 upshift. This condition can occur on Bravadas, 9-7X's and Rainiers NP4 Full time AWD. This will only happen in Trailblazers and Envoys NP8 when AWD (auto mode) is selected. When viewed through the TECH II, misfire counts may be occurring but not enough to set a misfire DTC. The concern will be eliminated in Bravadas and Rainiers with the ATC fuse removed or in Trailblazers and Envoys when 2hi or 4hi is selected.

Inspect tire pressures and adjust as necessary. Swap the wheels and tires from another identically built vehicle that does not exhibit the concern. If swapping the wheels and tires does not improve the condition, drain and fill the transfer case with AutoTrac II fluid and re-evaluate the condition.

This is likely a characteristic of the vehicle and some degree of this condition should be expected on all of these vehicles. Comparing this vehicle to an identical vehicle with similar mileage should verify this is a design characteristic.

Please follow this diagnostic or repair 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.