DTC 24 SET DURING CALIFORNIA STATE EMISSIONS TEST. GMC Truck Jimmy

SUBJECT: DTC 24 SET DURING CALIFORNIA STATE EMISSIONS TEST (NEW CALIBRATION)

MODELS: 1992 CHEVROLET AND GMC S/T TRUCKS WITH 4.3L V6 ENGINE (VIN Z - RPO LB4) AND MANUAL ONLY TRANSMISSION (RPO MY2)

THIS BULLETIN APPLIES TO CALIFORNIA ONLY.

CONDITION:

SOME CALIFORNIA ONLY OWNERS MAY EXPERIENCE THE MALFUNCTION INDICATOR LAMP (CHECK ENGINE LIGHT) ILLUMINATES AND MAY SET A DTC 24 (VSS CIRCUIT FAULT) DURING A CALIFORNIA STATE EMISSIONS TEST.

CAUSE:

SOME VEHICLES WITH MILEAGE ACCUMULATION MAY HAVE MAP LEVELS BELOW THE 25 KPA THRESHOLD DURING THE 2500 RPM, TRANSMISSION IN NEUTRAL, PORTION OF THE TEST.

THESE CONDITIONS ARE USED TO IDENTIFY A COASTDOWN CONDITION, DURING WHICH THERE SHOULD BE SOME VEHICLE ROAD SPEED. SINCE THERE IS NO VEHICLE ROAD SPEED DURING THE EMISSIONS TEST, THE DTC 24 MAY BE SET.

CORRECTION:

CALIBRATIONS, WITH THE MAP THRESHOLD REDUCED FROM 25 KPA TO 20 KPA FOR THE DTC 24 TEST, HAVE BEEN RELEASED. THE NEW CALIBRATIONS DO NOT AFFECT VEHICLE EMISSIONS, AND WILL DETECT A TRUE VEHICLE SPEED SENSOR (VSS) MALFUNCTION.

THE FOLLOWING MEMCALS ARE AVAILABLE FOR CALIFORNIA VEHICLES DESCRIBED WITH THE CONDITION DESCRIBED ABOVE:

APPLICATION OLD NEW NEW SERVICE AXLE RATIO B/C -- CAL. I.D. B/C -- CAL. I.D. MEMCAL P/N ___________ ________________ ________________ ___________

2.73 (GU2) BHSF -- 6145 BRJL -- 6845 16226742 3.08 (GU4) BHSH -- 6155 BRJM -- 6855 16226744 3.42 (GU6) BHSJ -- 6165 BRJN -- 6865 16226747

SERVICE INFORMATION SERVICE MEMCALS ARE AVAILABLE FROM GMSPO AS OF JULY 24, 1995.

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION NUMBER: J6364 LABOR OPERATION TIME: 0.8 HR.

FIGURES: 0 ATTACHMENTS: 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.