Intermittent Hesitation, Stumble or Idle Stall after Soak, Harsh 1-2 Shift, Slipping 1-2 Shift Followed by a Harsh Engagement (Reprogram PCM)

Some customers may comment on an intermittent hesitation/stumble or idle stall within minutes of starting after the vehicle has been sitting for several hours. Additionally, some customers with a 2003 model year vehicle may comment on a harsh 1-2 shift or 1-2 slip shift that has a bump feeling when 2nd gear engages.

This condition may be caused by the EVAP diagnostic test as it opens the purge valve for a few seconds and then closes it to verify proper emission sensor operation. If the purge canister is saturated, the EVAP system on-board diagnostic test may cause the vehicle to correct for a rich condition from the canister. The vehicle would then become lean when the purge valve closes at the completion of the test. This condition occurs primarily with high RVP fuel and after the vehicle sits for several hours in a warm ambient, above 21°C (70°F). A customer who takes short trips is more likely to experience this condition, as they don't have the drive cycle that would allow the purge canister to fully re-circulate the fuel vapor.

For Hesitation, Stumble or Idle Stall:

Follow the SI diagnostics for the stall/stumble condition. If the result is no trouble found, then reprogram the module with the latest calibration.

For Harsh or Slipping Shifts on 2003 Model Year vehicles:

Reprogram the module with the latest calibration.

The calibrations listed are electronic calibrations and are NOT available from GMSPO. Calibrations will be available from Techline starting September 2003, on the TIS 2003 Disc 10.0 CD ROM.

For vehicles repaired under warranty, use the appropriate labor operation below: