FOUR WHEEL DRIVE INOPERATIVE (REPLACE TRANSFER CASE SYNC.. GMC Truck GMC K Pickup

SUBJECT: FOUR WHEEL DRIVE INOPERATIVE (REPLACE TRANSFER CASE SYNCHRONIZER RELAY/INSTALL DIODE)

MODELS: 1988-98 CHEVROLET AND GMC K3 MODELS WITH ELECTRONIC FRONT AXLE ACTUATOR

CONDITION:

SOME OWNERS MAY COMMENT THAT FOUR WHEEL DRIVE DOES NOT ENGAGE AFTER INSTALLATION OF THE UPDATED FOUR WHEEL DRIVE FAST ACTUATOR.

CAUSE:

WHEN THE TRANSFER CASE IS SHIFTED INTO FOUR WHEEL DRIVE, THEN SHIFTED BACK TO TWO WHEEL DRIVE BEFORE THE AXLE ENGAGES, APPROXIMATELY 7 SECONDS, A VOLTAGE SPIKE MAY RESULT IN FAILURE OF THE TRANSFER CASE SYNCHRONIZER RELAY.

CORRECTION:

REPLACE THE TRANSFER CASE SHIFT SYNCHRONIZER RELAY AND INSTALL A DIODE TO PROTECT THE CIRCUIT. USE THE PART NUMBERS LISTED BELOW. USE THE FOLLOWING SERVICE PROCEDURE.

SERVICE PROCEDURE

1. INSTALL THE DIODE ON THE RELAY BRANCH APPROXIMATELY 50 MM (2 IN) FROM THE BASE OF THE RELAY CONNECTOR.

2. PLACE CKT 150 (BLK) LEAD TO THE "X" (ANODE) CAVITY OF THE DIODE. PLACE CKT 1297 (RED) LEAD TO THE "Y" (CATHODE) CAVITY OF THE DIODE. "X" AND "Y" SIDES OF THE DIODE ARE LABELED ON THE CASE. DO NOT CROSS THE POSITIONS OF THE CIRCUITS IN THE DIODE.

3. TAPE WIRE LEADS TO THE TABS PROVIDED ON THE DIODE. THEN TAPE OVER THE DIODE AND LEADS ON THE RELAY BRANCH.

PART INFORMATION:

P/N DESCRIPTION QTY --- ----------- --- 12110147 DIODE 1 12182086 RELAY, SYNCHRONIZER SHIFT 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION LABOR TIME --------- ---------- K4125 0.2 HR

FIGURES: 00 ATTACHMENTS: 00

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.