FLICKERING CHECK ENGINE LIGHT IMPROPER OXYGEN SENSOR/WIRING

A QUICKLY FLASHING OR "FLICKERING" CHECK ENGINE LIGHT ACCOMPANIED BY AN ERRATIC MPG SENTINEL DISPLAY MAY BE CAUSED BY AN IMPROPERLY FUNCTIONING OXYGEN SENSOR OR OXYGEN SENSOR CIRCUITRY. THESE CONDITIONS MAY SET A DIAGNOSTIC CODE 44; HOWEVER, A DIAGNOSTIC CODE WILL USUALLY NOT BE SET, AND THE PERFORMANCE OF THE VEHICLE GENERALLY WILL NOT BE AFFECTED. DETAILED DIAGNOSTIC PROCEDURES FOR THESE CONDITIONS ARE OUTLINED IN THIS BULLETIN. CONDITION 1 - IMPROPERLY FUNCTIONING OXYGEN SENSOR THIS CONDITION USUALLY OCCURS DURING A DECELERATION, ESPECIALLY FROM SPEEDS ABOVE 58 MPH WHILE IN THE 8 CYLINDER MODE. THE OXYGEN SENSOR MAY BE INDICATING TOO LEAN, SENDING A NEGATIVE VOLTAGE TO THE ECM DURING THIS NORMALLY LEAN SITUATION. THIS CAN BE VERIFIED BY OBSERVING PARAMETER 07 WHILE IN DIAGNOSTIC DISPLAY MODE (THE CHECK ENGINE LIGHT WILL NOT FLICKER AND DIAGNOSTIC CODES CANNOT BE SET WHILE IN DIAGNOSTIC DISPLAY MODE). A VEHICLE WITH A CONTAMINATED OR MALFUNCTIONING OXYGEN SENSOR WILL DROP TO A PARAMETER 07 VALUE OF 0 AND WILL HOLD AT THAT VALUE DURING DECELERATION; WHEREAS IN A NORMAL CAR, THE PARAMETER VALUE WILL DROP TO ZERO ONLY MOMENTARILY. THIS CONDITION MAY BE CAUSED BY AN IMPROPERLY POSITIONED OXYGEN SENSOR BOOT OR A CONTAMINATED OXYGEN SENSOR. THE CONTAMINATION MAY ORIGINATE FROM: 1.LEADED GASOLINE. 2.CONTAMINATED FUEL. 3.BY-PRODUCTS FROM THE CURING PROCESS OF NON-GM APPROVED RTV COMPOUNDS USED TO SEAL ENGINE VALVE COVERS. CADILLAC RECOMMENDS USING PART NUMBER 1052751 (3 OUNCE TUBE). 4.SILICONE OXYGEN SENSOR BOOT MATERIAL RESULTING FROM EXCESSIVE ENGINE HEAT CAUSING THE BOOT TO DECOMPOSE. 5.ENGINE OIL LEAKS RESULTING IN OIL GETTING INTO THE AMBIENT AIR REFERENCE CHAMBER OF THE OXYGEN SENSOR. FUEL CONTAMINATION OR EXCESSIVE ENGINE EXHAUST MANIFOLD TEMPERATURES SHOULD BE SUSPECTED IF A VEHICLE REQUIRES REPEATED REPLACEMENT OF THE OXYGEN SENSOR. CONDITION 2 - IMPROPER OXYGEN SENSOR WIRING (CIRCUIT 413) WHEN CIRCUIT 413, THE OXYGEN SENSOR GROUND OPENS OR HAS A POOR CONTACT AT A TERMINAL, A FLICKERING CHECK ENGINE LIGHT VERY SIMILAR TO THAT CAUSED BY THE OXYGEN SENSOR WILL OCCUR; HOWEVER, THIS CONDITION WILL OCCUR RANDOMLY OR CONTINUOUSLY, RATHER THAN DURING DECELERATION. IT MAY NOT BE POSSIBLE TO ENTER DIAGNOSTICS WHILE THIS CONDITION IS OCCURRING. IF THE CONDITION IS OCCURRING INTERMITTENTLY, MANIPULATE THE RELATED WIRING WHILE OBSERVING ENGINE DATA PARAMETER 07 AT PART THROTTLE WITH THE ENGINE WARM. IF THE CONDITION IS INDUCED, THE PARAMETER READING WILL DROP TO ZERO AND REMAIN THERE. PARTICULAR ATTENTION SHOULD BE GIVEN TO: 1. THE ENVIRONMENTAL BULKHEAD CONNECTOR, 2. THE ECM CONNECTOR, 3. THE OXYGEN SENSOR CONNECTORS, AND 4. BOTH CONNECTIONS TO ENGINE GROUND. THE GROUND CONNECTIONS, LOCATED ON STUDS NEAR THE NUMBER 1 CYLINDER, MUST BE SECURE AND CONTAIN STAR WASHERS. NOTICE: AN OHMMETER OR TEST LAMP SHOULD NOT BE USED TO CHECK CONTINUITY OF OXYGEN SENSOR CIRCUITS WITH THE OXYGEN SENSOR OR ECM CONNECTED AS THIS WILL DAMAGE THE OXYGEN SENSOR AND/OR PROVIDE FALSE READINGS. THESE CONNECTIONS MUST BE PARTICULARLY SECURE DUE TO THE LOW VOLTAGE AND CURRENT INVOLVED.

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.