QUESTION: My "service stability system" light has come on. I was not aware this car had one and am unable to find information in the operator’s manual. I phoned a local dealer and was quoted $142, and AAA quoted by phone $117. Quite a difference.

A diagnostic check is needed per dealer. Why? The dealer said it could be caused by different causes. I don’t understand. After receiving the above message, it seems they should know the cause. This is a 2005 Buick Park Avenue Ultra, with 20,720 miles.

—Clyde D.

ANSWER: Let’s start with a quick overview of your vehicle stability enhancement system.

This important safety system utilizes information from several vehicle systems as well as three dedicated sensors — lateral acceleration, yaw rate, and steering wheel position — to infer the Buick isn’t turning as the steering wheel has requested. If yaw error, or incorrect turning, is indicated, vehicle power may be altered and one front brake applied to bring the car back on course.

This shouldn’t be too difficult to resolve; there will be a diagnostic trouble code stored that will indicate a specific section of the system to check. The system is managed by the electronic brake control module, which sends a message to the instrument panel cluster when a component or circuit fault is encountered. Since no other malfunction indicators were illuminated, it sounds like a fault may be present in one of the three mentioned sensors or their circuits, rather than elsewhere.

It’s impractical to quote a final price to fix this over the phone, as a variety of faults could be the cause. The prices you were quoted were surely just to check and advise of the repairs needed. The dealer’s information is on target, as a diagnostic test drive and check is needed to validate and diagnose the trouble code found.

After retrieving the diagnostic trouble code, the technician researches applicable diagnostic aids and conditions under which the fault can be detected. A careful test of the steering wheel sensor is performed during a low speed, straight-line maneuver while observing scan tool sensor information. The system is next tested without the scan tool by driving at highway speeds, on various rough roads and during high steering wheel angle cloverleaf and parking lot maneuvers, in an attempt to duplicate the fault and re-illuminate the indicator.

The three sensors, while internally quite sophisticated, are supported by very straightforward circuitry, and are similar to typical "check engine" light issues in the way they are tested. Should the lateral accelerometer require replacement, it’s located beneath the rear seat, and the yaw rate sensor is inside the trunk, attached to the bottom of the package shelf. The steering wheel position sensor is more difficult to replace. Parts prices range from moderate to scary. Let’s hope for an easy-to-fix faulty connection with no parts needed.

It may be worth a shot to ring up Buick Customer Relations at 800-521-7300 and ask for repair assistance once the fault has been identified. With the low miles accrued on this vehicle safety system, it’s possible they might participate in some way.