Downhill Cruise Control Surge - keywords buck chuggle decelerate driveability flare gas L18 L33 L59 LM7 LQ4 LQ9 LR4 performance

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

Surge, chuggle or buck while driving downhill (Hilly or Mountainous Terrain) at highway speeds with the cruise control set.

If there are no DTCs stored and this does not happen with the cruise control in the off position, no repair attempts should be made as this is a normal characteristic of the vehicle.

Important: If comparing to a like vehicle make sure the vehicle is exactly the same year, make, model, engine, transmission, axle ratio, tire size, as the owners and that the vehicle is driven at the same MPH the surge occurs and same hill/mountain.

Note: The dealer should also review the "using cruise control on hills" section of the Owner's manual. This section states the following about using the cruise control while driving downhill: (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.