Intermittent Unwanted Dynamic Rear Proportioning (DRP) Event - keywords ABS active brake hydraulic pulsation WSS

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

Unwanted Dynamic Rear Proportioning (DRP) Activations during braking above 42mph. Brake Pedal feedback and ABS pump motor noise during straight line braking above 42MPH. During this condition the ABS / DRP data list may indicate DRP active. This condition is usually duplicated during every deceleration above 42MPH as long as the brake switch is on. This condition can be caused by excessive circumference variation in one or more of the tires. The vehicles listed incorporate a specific algorithm that activates the DRP system during cornering above 42 MPH. If one or more of the tires sizes are incorrect for the vehicle, the difference in tire circumference may cause the EBTCM to interpret that the vehicle is cornering even though it is traveling straight. This results in unwanted activations of the DRP system.

Inspect all 4 tires for being the same/correct size, brand, model and tread pattern. If all 4 tires seem to be the same, drive the vehicle and monitor the 4 wheel speed sensors on the ABS / DRP data list. Sometimes, one wheel will read slightly faster or slower (+/- 2mph) than the others at straight-line highway speeds. If scan tool data supports it, rotate the suspected tire to a different corner of the vehicle, and again monitor the data list at highway speeds.

Replace the affected tire(s). Typically one of the tires was recently replaced, and the exact tire size and brand was not matched. There have been a few instances where an incorrect tire was installed at the assembly plant. Also, occasional "excessive" circumference variation for tires which are the same size has also been documented.

If there is any doubt or the diagnostics do not conclusively pinpoint the tires as the cause of the concern, swap the tire/wheel assemblies off of an identical vehicle and evaluate the results. This step can avoid the cost of unnecessary tire replacement for instances where the diagnostics do not clearly define the root cause.

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.