FOUR WHEEL DRIVE HI RANGE DOES NOT ENGAGE DURING COLD WEATHER. Chevrolet Chevy K Pickup

SUBJECT: FOUR WHEEL DRIVE HI RANGE DOES NOT ENGAGE DURING COLD WEATHER (REPLACE FRONT DIFFERENTIAL GEAR LUBE)

MODELS: 1996-97 CHEVROLET AND GMC K1, K2 MODELS WITH ELECTRIC SHIFT TRANSFER CASE (RPO NP1)

CONDITION:

SOME OWNERS MAY REPORT THAT IF THE AMBIENT TEMPERATURE IS 10 DEGREES F (-12C) OR COLDER, WHEN ATTEMPTING TO SHIFT THE TRANSFER CASE FROM 2HI TO 4HI WHILE THE TRUCK IS MOVING, THE 2HI INDICATOR LIGHT REMAINS ON AND THE 4HI LIGHT FLASHES FOR AN EXTENDED PERIOD OF TIME BUT 4HI DOES NOT ENGAGE.

CAUSE:

HIGH VISCOSITY OF THE FRONT AXLE GEAR LUBE WHEN COLD. THIS HIGH VISCOSITY DELAYS OR PREVENTS THE FRONT PROPELLER SHAFT FROM ROTATING AT THE SPEED REQUIRED FOR FRONT AXLE ENGAGEMENT.

CORRECTION:

REPLACE THE FRONT DIFFERENTIAL GEAR LUBE WITH SAE 75W-90 SYNTHETIC GEAR LUBE (P/N 12345836). SYNTHETIC GEAR LUBE HAS A LOWER VISCOSITY THAN NON-SYNTHETIC IN COLD WEATHER CONDITIONS.

SERVICE PROCEDURE:

BEFORE INSTALLING THE SYNTHETIC GEAR LUBE, DRAIN AND REFILL THE DIFFERENTIAL WITH FRESH NON-SYNTHETIC GEAR LUBE AND DRIVE THE TRUCK NO LESS THAN 3 MILES. THEN DRAIN THE DIFFERENTIAL AND REFILL IT TO THE LEVEL OF THE OIL FILL HOLE WITH THE SPECIFIED SYNTHETIC GEAR LUBE. THIS IS NECESSARY TO ENSURE THAT THE DIFFERENTIAL IS CLEAN BEFORE ADDING THE SYNTHETIC GEAR LUBE. FRONT DIFFERENTIAL GEAR LUBE CAPACITY IS AS FOLLOWS: - 8-1/4" AXLE 1.6 LITERS (1.75 QT.) - 9-1/4" AXLE 2.1 LITERS (2.2 QT.)

PART INFORMATION:

P/N DESCRIPTION 12345836 SAE 75W-90 SYNTHETIC GEAR LUBE, 1 QT BOTTLE

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME F 2022 FRONT DIFFERENTIAL, OIL 0.6 HR

IMPORTANT: LABOR OPERATION IS CODED TO BASE VEHICLE COVERAGE IN THE WARRANTY SYSTEM. ZONE REPRESENTIVE APPROVAL MAY BE REQUIRED FOR DUPLICATE LABOR OPERATION.

FIGURES: 0

CAPTIONS: 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.