COLD TEMPERATURE VCM RESET CAUSING LOSS OF DTC'S. GMC Truck Jimmy

REVISION: 05/23/96

THIS BULLETIN IS BEING REVISED TO CHANGE WITH RPO K29 TO WITHOUT RPO K29 IN THE MODELS SECTION. PLEASE DISCARD BULLETIN 57-65-29 (SECTION 6E - ENGINE FUEL AND EMISSION). **********************************************************************

SUBJECT: COLD TEMPERATURE VCM RESET CAUSING LOSS OF DTC'S (UPDATE CALIBRATION)

MODELS: 1995 CHEVROLET AND GMC TRUCK S/T MODELS WITH 4.3L ENGINE (VIN W - RPO L35) WITHOUT RPO K29

CONDITION:

SOME CUSTOMERS MAY BRING THEIR VEHICLE IN FOR SERVICE WITH THE COMMENT THAT THE MIL LIGHT (SES) IS ILLUMINATED.

WHEN THE SERVICE TECHNICIAN LOOKS FOR DIAGNOSTIC TROUBLE CODES (USING A TECH 1), THERE ARE NONE STORED.

THIS PROBLEM ONLY OCCURS DURING COLD WEATHER VEHICLE OPERATION, TYPICALLY IN THE NORTHERN CLIMATES.

CAUSE:

DURING A COLD WEATHER START CONDITION, IF THE BATTERY VOLTAGE TEMPORARILY DROPS BELOW 9 VOLTS, AND THE IGNITION SWITCH IS ROTATED RAPIDLY TO THE CRANK POSITION, THE VCM MAY RESET CAUSING ANY STORED FAULT DTCS TO BE ERASED.

NOTICE: LOW BATTERY VOLTAGE DURING A START PROCEDURE MAY BE A SYMPTOM OF ANOTHER PROBLEM (DISCHARGED BATTERY, WIRING OR CONNECTIONS, CHARGING SYSTEM PERFORMANCE, ETC.).

CORRECTION:

NEW SOFTWARE HAS BEEN RELEASED TO ADDRESS THIS CONDITION. UPDATED CALIBRATIONS WERE RELEASED TO VEHICLE ASSEMBLY PLANTS JANUARY, 1995.

1 - HAVE THE CALIBRATION I.D. CHECKED WITH A TECH 1. 2 - VEHICLES IDENTIFIED AS HAVING THE OLD CALIBRATION SHOULD BE UPDATED WITH THE NEW FLASH CALIBRATION.

CALIBRATION INFORMATION THE CALIBRATIONS LISTED BELOW ARE FLASH CALIBRATIONS AND NOT AVAILABLE FROM GMSPO. SERVICE FLASH CALIBRATIONS ARE AVAILABLE STARTING WITH THE JULY 1995 CD ROM.

FEDERAL AND CALIFORNIA

MODEL - BODY STYLE ENGINE TRANS. EMISSION OLD CAL. NEW CAL.

S/T - L35 MANUAL FEDERAL 16206783 16206790 ALL BODIES UNLEADED FUEL

S/T - L35 AUTO FEDERAL 16206785 16206791 ALL BODIES UNLEADED OR FUEL 16206787

S/T - L35 AUTO CALIF. 16206784 16206792 ALL BODIES UNLEADED OR FUEL 16206786

EXPORT

MODEL - BODY STYLE ENGINE TRANS. EMISSION OLD CAL. NEW CAL.

S/T - L35 MANUAL UNLEADED 16206783 16206789 ALL BODIES FUEL

S/T - L35 AUTO UNLEADED 16206785 16215623 ALL BODIES FUEL

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE: LABOR OPERATION: J-6355 LABOR TIME: 0.3 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.