DIESEL EGR VALVE FUNCTIONAL CHECK

IT IS POSSIBLE FOR A TECHNICIAN TO BE DECEIVED BY ONLY CHECKING EGR VALVE FUNCTION AS OUTLINED IN THE SERVICE MANUALS. THE MANUALS RECOMMEND THAT A MEASURED EXTERNAL VACUUM SOURCE BE APPLIED TO CHECK FOR VALVE OPENING AND CLOSING POINTS. WHILE THE VALVE DIAPHRAGM MAY OPEN AND CLOSE AT THE PROPER VACUUM VALVES, THERE MAY BE OTHER MALFUNCTIONS WITH THE VALVE THAT MAY CAUSE IT TO BE INOPERATIVE. PROPER OPERATION OF THE EGR VALVE CAN BE DETECTED BY A DIFFERENCE IN NOISE LEVEL. WITH THE ENGINE AT IDLE, OPERATING TEMPERATURE, DRIVE WHEELS BLOCKED, PARKING BRAKE SET, AND TRANSMISSION IN "P" (PARK), REMOVE THE AIR CLEANER COVER. WHILE USING AN EXTERNAL MEASURED VACUUM SOURCE, PERFORM THE EGR VALVE FUNCTIONAL CHECK THAT IS IN THE CHASSIS SERVICE MANUAL. WHEN THE VALVE IS OPEN, YOU SHOULD HEAR THE EXHAUST GASES PASSING THROUGH THE EGR VALVE AND INTO THE AIR CROSSOVER. WHEN VACUUM IS BLED OFF AND THE VALVE IS CLOSED, THERE SHOULD BE A NOTICEABLE REDUCTION OF SOUND HEARD WITHIN THE AIR CROSSOVER SINCE EXHAUST GASES ARE NO LONGER FLOWING INTO IT. IF A SOUND DIFFERENCE IS NOT HEARD, REMOVE THE EGR VALVE ASSEMBLY, AND INSPECT THE VALVE AND VALVE SEAT.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.