NEW ECM TEST PROCEDURES ALL ECM EQUIPPED VEHICLES

PURPOSE OF THIS BULLETIN IS TO INTRODUCE NEW ECM TEST PROCEDURES TO REDUCE THE POSSIBILITY OF MULTIPLE ECM FAILURES ON ANY ONE VEHICLE. SINCE 1982, MOST ECMS HAVE USED AN INTEGRATED CIRCUIT (IC) IN PLACE OF SEPARATE TRANSISTORS TO TURN "ON" OR "OFF" DIFFERENT COMPONENTS CONTROLLED BY THE ECM. THESE ICS ARE CALLED QUAD DRIVERS (QDR). EACH QDR HAS FOUR SEPARATE OUTPUTS, MEANING IT CAN TURN "ON" OR "OFF" FOUR DIFFERENT ITEMS INDEPENDENTLY. A FAILED QDR USUALLY RESULTS IN AN ECM OUTPUT BECOMING EITHER SHORTED TO GROUND OR OPEN. MANY TIMES ALL FOUR QDR OUTPUTS WILL BE INOPERATIVE IF JUST ONE VEHICLE CIRCUIT IF FAULTY. THE REVISED DIAGNOSTIC INCORPORATES NEW TEST PROCEDURES DESIGNED TO IDENTIFY A DAMAGED QDR. ONCE IDENTIFIED, THE CIRCUIT MUST BE REPAIRED TO REDUCE THE INCIDENCE OF REPEAT ECM FAILURES. THIS CHART REPLACES THE CURRENT SERVICE MANUAL PROCEDURE FOR EITHER: 1. CHART C-1 ECM REPLACEMENT CHECK OR 2. ANY DIAGNOSTIC CHART WHERE "REPLACE ECM" IS THE CONCLUSION, ESPECIALLY IF A FOOTNOTE INDICATES CHECKING CERTAIN CIRCUITS FOR LESS THAN 20 OHMS RESISTANCE. IT IS STRONGLY SUGGESTED THAT THIS CHART BE USED WHENEVER AN ECM REPLACEMENT IS INDICATED FOR 1982 THRU 1987 VEHICLES.

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.