Phasing Drone Moan Or Vibration At approximately 50MPH Or 1200-1300 RPM - keywords accelerate light throttle

This PI was superseded to update model years and EVA diagnostics. Please discard PIP4435A.

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

Some customers may comment of a boom, moan or vibration during light acceleration which phases in and out in intensity.

The condition may be most noticeable at about 50 mph (80 kph), or 1200 - 1300 rpm, and occurs over a speed range of 3 to 5 mph (5 to 8 kph). This condition can be caused by the rear axle assembly responding to frequencies generated by the transmission when the Torque Converter Clutch (TCC) is engaged.

Perform the procedure in SI Document ID 1578733: "Vibration Analysis - Road Testing". This condition can be identified as a third-order engine disturbance by using the J 38792-A, Electronic Vibration Analyzer (EVA) 2. Verify the concern by duplicating the condition and then commanding the TCC off with the Tech 2. If the condition is verified, it may be reduced or eliminated by indexing the propshaft. Ensure that the rear axle damper is in place and not grounded out.

If the damper is in place and indexing the prop shaft does not eliminate the concern do not attempt any further repairs at this time. Engineering is aware of this concern and is developing a repair at this time. Further repair information will be available when a procedure is developed and verified.

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.