SMU - SECTION 3 - DRIVEABILITY AND EMISSIONS

SUBJECT: SERVICE MANUAL UPDATE-SECTION 3-DRIVEABILITY AND EMISSIONS CONTROL MODULE SYSTEMS-REVISED ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

MODELS: 1993 CHEVROLET AND GMC TRUCK C/K AND G MODELS WITH 6.2L DIESEL ENGINE (VIN C-RPO LH6)

THE ON-BOARD DIAGNOSTIC SYSTEM CHECK FOR 1993 VEHICLES WITH A PCM DOES NOT FUNCTION LIKE A "TYPICAL" OBD SYSTEM CHECK. THE PROPER OPERATION OF THE SYSTEM IS AS FOLLOWS: * IGNITION "ON," ENGINE "OFF" - MIL WILL ONLY COME "ON" FOR 2 SECONDS DURING BULB CHECK. (PCM MUST POWER DOWN TO GET ANOTHER MIL BULB CHECK). * IGNITION "ON," ENGINE "OFF" - THE MIL WILL NOT FLASH DTC 12 WHEN DIAGNOSTIC TERMINAL IS GROUNDED (A AND B TERMINALS AT DLC), BUT WILL FLASH DIAGNOSTIC TROUBLE CODES IF PRESENT. * THE TECH 1 WILL NOT FLASH THE MIL WHEN COMMANDED DURING THE OBD SYSTEM CHECK.

CORRECTIONS * A NEW DIAGNOSTIC CHART FOR THE ON-BOARD DIAGNOSTIC SYSTEM CHECK HAS BEEN CREATED TO PROPERLY PERFORM OBD SYSTEM CHECK. * CHART A-2, FACING PAGE AND DIAGNOSTIC CHART MUST BE DISREGARDED.

THIS INFORMATION REPLACES THE INFORMATION FOUND IN SECTION 3, UNDER ON-BOARD DIAGNOSTIC SYSTEM CHECK AND CHART A-2.

FIGURES: 00 ATTACHMENTS: 01

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. COPYRIGHT 1995 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.