Surge Downhill with Cruise Control On - Reprogram PCM - keywords buck calibration chuggle decelerate deceleration erratic flare

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

On rare occasions, a buck, chuggle, or surge may be experienced while traveling down a long grade with the cruise control on at highway speeds. Typically, this will occur in mountainous regions while descending long grades.

If this does not occur with the cruise control off or when traveling on flat road surfaces with the cruise control on and there are no DTCs stored, reprogram the PCM with the latest TIS2000 calibrations, which are designed to improve this concern under most operating conditions.

If the above concern is still present after reprogramming the PCM, no additional repairs should be performed. Instead, the cruise control should be disabled when descending long grades.

Additionally, the "using cruise control on hills" section of the owner's manual, found on page 3-14 (Bravada, Rainier and TrailBlazer) or 3-15 (Envoy), states: "When going downhill, you may have to brake or shift to a lower gear to keep your speed down. Of course, applying the brake takes you out of cruise control. Many drivers find this to be too much trouble and don't use cruise control on steep hills."

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.