LACK OF WARM AIR FROM HEATER OR DEFROSTER

SOME EARLY PRODUCTION 1987 'R' AND 'V' TRUCKS EQUIPPED WITH L03 AND L05 ENGINES THAT WERE BUILT AT THE JANESVILLE PLANT MAY HAVE A BLOCKAGE IN THE INTAKE MANIFOLD THAT COULD RESTRICT COOLANT FLOW TO THE HEATER CORE AND COULD CAUSE LOW OR NO HEAT FROM THE VEHICLE HEATER. THIS CONDITION WAS CORRECTED IN PRODUCTION EFFECTIVE WITH VIN BREAKPOINTS J103535 (CHEVROLET) AND (J501393) GMC. IF THIS CONDITION IS ENCOUNTERED, IT CAN BE CORRECTED USING THE FOLLOWING MANIFOLD REPAIR PROCEDURE. (REFER TO FIGURE NO. 1 FOR ADDITIONAL DETAILS). 1. DRAIN ALL COOLANT FROM RADIATOR. CAUTION: NEVER REMOVE THE RADIATOR CAP FROM A HOT RADIATOR, AS PERSONAL INJURY MAY OCCUR. REMOVE THE CAP SLOWLY TO RELIEVE ANY PRESSURE IN THE COOLANT SYSTEM. 2. REMOVE PLUG FROM INLET MANIFOLD (3/8" ALLEN WRENCH) LOCATED TO THE LEFT (DRIVER'S SIDE) AND REARWARD OF THE TBI UNIT (SEE FIGURE 1). 3. PROBE WITH A 5/16" ROD. ROD SHOULD DROP INTO HOLE TO A DEPTH OF 4 INCHES. 4. IF PROBING SHOWS NO BLOCKAGE, THE PLUG SHOULD BE REINSTALLED. THE PLUG THREADS MUST BE COATED WITH PIPE SEALANT, P/N 1052080, OR EQUIVALENT. INSTALL THE PLUG SO THAT THE TOP OF THE PLUG IS EVEN WITH THE MANIFOLD. 5. IF BLOCKAGE IS FOUND (FOR EXAMPLE, THE PROBE WILL ONLY GO TO A DEPTH OF 3 INCHES), CONTINUE WITH THE FOLLOWING STEPS: 6. INSERT A 7/16" DIAMETER ROD (3/8" DRIVE EXTENSION - SOCKET END DOWN) INTO HOLE AND TAP WITH HAMMER TO BREAK BLOCKAGE FREE, BEING CAREFUL TO TRAP THE BROKEN FREE MATERIAL AT THE BOTTOM OF THE HOLE. 7. USING A WET VACUUM WITH AN 5/8" DIAMETER SUCTION HOSE INSERTED THROUGH HOLE, RETRIEVE BROKEN FREE MATERIAL. NOTE: IF "BROKEN FREE" MATERIAL CANNOT BE RETRIEVED, THE INTAKE MANIFOLD SHOULD BE REPLACED. 8. VERIFY HOLE IS OPEN BY RE-PROBING WITH 5/16" DIAMETER ROD. 9. RE-INSTALL PLUG AND REFILL SYSTEM WITH COOLANT PLUG THREADS MUST BE COATED WITH PIPE SEALANT P/N 1052080. INSTALL THE PLUG UNTIL THE TOP OF THE PLUG IS EVEN WITH THE MANIFOLD. 10. VERIFY HEATER OPERATION. TIME TO VERIFY PASSAGE IS OPEN IS .5 HR. TIME TO INSPECT PASSAGE AND REMOVE BLOCKAGE IS .6 HR. USE LABOR OPERATION T7310 WHEN SUBMITTING CLAIMS FOR THIS PROCEDURE.

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.