RATTLING NOISE ON ACCELERATION/TRANSMISSION. GMC Truck Safari

SUBJECT: RATTLING NOISE ON ACCELERATION/TRANSMISSION STARTING OUT IN 3RD GEAR (PROVIDE CLEARANCE OR REPLACE EXHAUST CROSSOVER)

MODELS: 1993-94 CHEVROLET AND GMC TRUCK M/L VAN 1994 CHEVROLET AND GMC TRUCK T MODELS 1994 OLDSMOBILE BRAVADA WITH 4.3L ENGINES (VINS W, Z - RPOS L35, LB4)

CONDITION:

CUSTOMERS MAY COMMENT ON ONE OR MORE OF THE FOLLOWING CONDITIONS: A RATTLING NOISE ON ACCELERATION, TRANSMISSION STARTING OUT IN 3RD GEAR (POSSIBLE DTC 66, 67, 81, 82) AND/OR DIAGNOSTIC TROUBLE CODES 13 OR 44.

CAUSE:

M/L VANS:

OXYGEN SENSOR AND/OR HARNESS PIGTAIL CONTACTING THE HEAT SHIELD DUE TO IMPROPER ROUTING OF THE HARNESS. SHARP EDGES OF THE HEAT SHIELD CUTS THROUGH THE WIRE INSULATION.

T TRUCKS:

THE RATTLE NOISE MAY BE THE OXYGEN SENSOR AND/OR HARNESS PIGTAIL CONTACTING THE HEAT SHIELD DUE TO THE MISPOSITIONING OF THE OXYGEN SENSOR MOUNTING BOSS. STARTING OUT IN 3RD GEAR MAY BE DUE TO THE PINK WIRE (CKT 39) SHORTING OUT AGAINST THE HEAT SHIELD CAUSING POWER TO BE INTERRUPTED TO THE TRANSMISSION CONTROL CIRCUIT PUTTING THE TRANSMISSION INTO BACKUP MODE (3RD GEAR STARTS). DIAGNOSTIC TROUBLE CODES 13 OR 44 MAY BE SET DUE TO THE OXYGEN SENSOR SIGNAL WIRE SHORTING TO OR CUT THROUGH BY THE HEAT SHIELD.

CORRECTION:

M/L VANS:

REFER TO THE "1993 M/L VAN ELECTRICAL DIAGRAMS AND DIAGNOSIS" MANUAL OR THE "1994 DRIVEABILITY, EMISSIONS AND ELECTRICAL DIAGNOSIS" MANUAL FOR CIRCUIT 39 SCHEMATICS. NORMAL CIRCUIT DIAGNOSTICS SHOULD BE PERFORMED FIRST IF THE PROBLEM IS CONSTANT. IF THE PROBLEM IS INTERMITTENT, AN INSPECTION OF CIRCUIT 39 (PINK/BLACK) IN THE AREA OF THE EXHAUST HEAT SHIELDS MAY LEAD TO THE PROBLEM. INSPECT THE OXYGEN SENSOR WIRING AND REPLACE THE SENSOR IF THE INSULATION HAS BEEN DAMAGED. RE-ROUTE WIRING HARNESS AS NEEDED TO PROTECT HARNESS. CLEAR ANY CODES AND TEST DRIVE.

T TRUCKS:

IF THE OXYGEN SENSOR IS CONTACTING THE HEAT SHIELD, THIS CONDITION CAN BE CORRECTED BY REPLACING THE EXHAUST CROSSOVER PIPE. IF THE OXYGEN SENSOR WIRE IS DAMAGED, THE OXYGEN SENSOR MUST ALSO BE REPLACED.

FOLLOW REGULAR SERVICE MANUAL PROCEDURES IN SECTION 3 OF THE 1993 OR 1994 "S/T TRUCK DRIVEABILITY, EMISSION AND ELECTRICAL DIAGNOSIS" MANUAL TO MAKE ABOVE REPAIRS. CLEAR ANY DIAGNOSTIC TROUBLE CODES AND TEST DRIVE.

SERVICE PARTS INFORMATION:

P/N DESCRIPTION QTY

10096129 SENSOR, OXYGEN (1993) 1 25133503 SENSOR, OXYGEN (1994) 1 15661132 PIPE, EXHAUST CROSSOVER (W/ ZR2) 1 15672887 PIPE, EXHAUST CROSSOVER (W/O ZR2) 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME J6372 SENSOR, OXYGEN - REPLACE USE PUBLISHED L2080 PIPE, CROSSOVER EXHAUST - REPLACE LABOR OPERATION TIME

FIGURES: 0

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.