Cadillac's dashboard vibration may be HVAC-related

Some 2003 Cadillac DeVille and Seville models may emit a humming noise from the dash when the temperature control is positioned on the hot setting and the blower motor is set to medium or high speed.

According to General Motors, the most probable cause of the anomaly is a restriction in the incoming airflow due to the positioning of the blower motor relative to the HVAC case. Reindexing the motor in the case is the quick fix.

Here's how to go about the job:

• Start by removing the right side sound insulator.
• Now get to the case and loosen the three blower motor retaining bolts.
• Slide the motor as far as it will go in the direction of the ventilation/cooling tube, hold the motor in this position, then tighten the three retaining bolts to 12 in. lbs.
• To complete the fix, reinstall the sound insulator, then start the car and turn on the HVAC system to ensure that the noise has been eliminated.

"Factory Fixes" is written by Jim DePalma, a 30-year veteran of the auto repair business who has served stints as a service manager, parts manager and ASE-certified technician. His column provides vehicle manufacturers' authentic factory technical service bulletins (TSBs) that have been condensed for easier reading. Mr. DePalma advises that techs always check with a dealer or repair information system for the latest revisions before starting to work on a vehicle. He can be reached via e-mail at tirebusiness[email protected].