FALSO HVAC HISTORY DTC B0408 &/OR HEATER AND A/C. Chevrolet S10 Pickup

SUBJECT: FALSE HVAC HISTORY DTC B0408 AND/OR HEATER + A/C TEMPERATURE CONTROL DOOR MOTOR BECOMES INOPERATIVE WHILE USING SCAN TOOL (DELAY CONNECTING SCAN TOOL FOR MODULE INITIALIZATION.)

MODELS: 1998 CHEVROLET AND GMC S/T UTILITY MODELS 1998 OLDSMOBILE BRAVADA WITH FRONT AUTO ELECTRONIC A/C (RPO C68)

CONDITION:

WHEN A TECHNICIAN IS PERFORMING HVAC DIAGNOSTICS USING A SCAN TOOL ON SOME EARLY PRODUCTION VEHICLES, DTC B0408, TEMPERATURE CONTROL #1 CIRCUIT MALFUNCTION, MAY BE PRESENT WITHOUT A CUSTOMER REPORT OF A RELATED CONCERN. IN ADDITION, WHEN THE SCAN TOOL IS HOOKED UP, THE HVAC TEMPERATURE CONTROL DOOR MOTOR MAY LOCK-UP AND NOT RESPOND TO COMMANDS FROM THE HTR + A/C CONTROL MODULE OR SCAN TOOL.

CAUSE:

VARIATIONS IN THE TEMPERATURE DOOR GASKET COMPRESSION MAY CAUSE A HISTORY DTC B0408 TO SET. USING A SCAN TOOL DURING HTR + A/C CONTROL MODULE INITIALIZATION** CAN CAUSE A SOFTWARE CONFLICT.

** INITIALIZATION OF THE HTR + A/C CONTROL MODULE OCCURS WHENEVER B+ IS REMOVED AND THEN RESTORED TO THE HTR + A/C CONTROL MODULE. DURING THIS SHORT 40 SECOND INITIALIZATION PROCESS, THE TEMPERATURE DOOR IS COMMANDED TO THE FULL MAXIMUM POSITION AND THEN TO THE FULL MINIMUM POSITION. THE HTR + A/C CONTROL MODULE RECORDS BOTH POSITIONS AND USES THEM TO DETERMINE TEMPERATURE DOOR SETTINGS BASED ON SELECTED TEMPERATURE SETTINGS. THIS PROCESS OCCURS ONCE EACH TIME B+ IS RESTORED TO THE HTR + A/C CONTROL MODULE. DO NOT SELECT OR USE THE SCAN TOOL HVAC MENU SELECTION DURING HTR + A/C CONTROL MODULE INITIALIZATION OR THE HTR + A/C CONTROL MODULE WILL NOT INITIALIZE PROPERLY.

CORRECTION:

1. TURN THE IGNITION ON. 2. RECORD MIX DOOR MAX AND MIN POSITION VALUES. 3. ROTATE TEMP CONTROL KNOB TO FULL HOT, NOTE AIR MIX ACTUAL VALUE. 4. ROTATE TEMP CONTROL KNOB TO FULL COLD, NOTE AIR MIX ACTUAL VALUE.

IN THE FULL HOT (MAX) AND FULL COLD (MIN) POSITIONS, COMPARE THE ACTUAL VALUE TO THE RECORDED VALUE. IF THE DIFFERENCE IS LESS THAN 10 FOR EITHER VALUE, DISREGARD THE HISTORY DTC B0408. IF THE DIFFERENCE IS GREATER THAN 10 FOR EITHER VALUE, REFER TO SECTION 1C IN THE SERVICE MANUAL FOR DIAGNOSTIC PROCEDURES.

IF THE HTR + A/C CONTROL INITIALIZATION HAS BEEN INTERRUPTED BY USE OF A SCAN TOOL AND THE HTR + A/C CONTROL IS NOT RESPONDING TO TEMPERATURE CHANGES:

1. TURN IGNITION OFF. 2. MAKE SURE A SCAN TOOL IS NOT CONNECTED TO THE DLC CONNECTOR. 3. REMOVE THE RDO BATT FUSE FOR 10 SECONDS AND THEN REINSTALL IT. 4. TURN IGNITION ON, WAIT 40 SECONDS FOR THE HEATER + A/C CONTROL MODULE TO COMPLETE THE INITIALIZATION PROCESS.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME N6030 HVAC ELECTRICAL - REPAIR USE PUBLISHED LABOR OPERATION TIME

FIGURES: 00 CAPTIONS: 00

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.