The cam sensor interrupter (magnet) may become demagnetized and/or fall off of the camshaft gear causing the Check Engine Light (Service Engine Soon) light to illuminate. On higher mileage vehicles it would be advisable to replace the timing chain and gears if this problem were to occur as the timing cover must be removed to replace the interrupter.Google+
Car Problem Reports
Buick Park Avenue Check Engine Light Due to Cam Sensor Interrupter Falling off Camshaft Gear
Buick Park Avenue Problem
Engine Affected: 3.8L V6
Visitor, 1991 Buick Park Avenue, 3.8L V6, 170,000 mi
Check engine light showed a code for camshaft positioning sensor circuit. Camshaft sensor magnet fell of the cam gear. Took cover off and replaced the magnet. Works like new!