4L80E Automatic Transmission and 7.4L Engine, No TCC Apply Supplement to TSB 99-06-04-016

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

The 4L80E automatic transmission may exhibit a condition of no TCC apply at highway speeds with no request for TCC from the VCM. The TCC will engage when commanded with a Tech 2 Scan Tool.

TSB 99-06-04-016 Engine Surge While Trailering (Reprogram VCM) should be reviewed. If a calibration from TSB 99-06-04-016 has been installed the TCC will engage in excess of 70 mph. The VCM can be reprogrammed with a non-improved trailer towing performance calibration which is selectable from the TIS 2000.

Please follow this diagnosis 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. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.

96 - 99 Chevrolet C2500 7.4 (L29) 4L80E (MT1)

96 - 99 Chevrolet K2500 7.4 (L29) 4L80E (MT1)

96 - 99 Chevrolet C3500 7.4 (L29) 4L80E (MT1)

96 - 99 Chevrolet K3500 7.4 (L29) 4L80E (MT1)

96 - 99 GMC C2500 7.4 (L29) 4L80E (MT1)

96 - 99 GMC K2500 7.4 (L29) 4L80E (MT1)

96 - 99 GMC C3500 7.4 (L29) 4L80E (MT1)

96 - 99 GMC K3500 7.4 (L29) 4L80E (MT1)