For 1990-2009 cars

# INFORMATION ON DIAGNOSING SIR DTC 24 ALL DERM SYSTEMS

#### SUBJECT: INFORMATION ON DIAGNOSING SIR DTC 24 - ALL DERM SYSTEMS

#### MODELS: 1993 AND PRIOR MODELS WITH SIR 1994-95 MODELS WITH SIR EXCEPT THOSE WITH SENSING AND DIAGNOSTIC MODULE (SDM)

WHEN DIAGNOSING AN SIR DTC 24, THE FOLLOWING DISCRIMINATING SENSOR CHECK SHOULD ALSO BE PERFORMED.

* UNPLUG DISCRIMINATING SENSOR * SENSOR MUST REMAIN BOLTED SECURELY TO VEHICLE CHASSIS. * MEASURE RESISTANCE FROM SENSOR PINS TO CHASSIS GROUND. - MUST BE GREATER THAN 2 MEG OHMS. IF NOT, THEN REPLACE THE SENSOR.

#### NOTE: FOR INTERMITTENT SIR DTC 24 CONCERNS, IT MAY BE HELPFUL TO WATER-SOAK THE DISCRIMINATING SENSOR BEFORE PERFORMING THE ABOVE TEST.

EXPERIENCE HAS SHOWN THAT DISCRIMINATING SENSORS ARE A LEADING CAUSE OF DTC SIR CODE 24 CONCERNS. THESE SENSORS CAN DEVELOP TWO SEPARATE CONDITIONS THAT WILL CAUSE DTC SIR CODE 24: 1) THE FIRST IS CAUSED BY A SHORTED INTERNAL RESISTOR AND IS ADDRESSED BY CURRENT SERVICE MANUAL PROCEDURES. 2) THE SECOND IS CAUSED BY A PARTIAL SHORT BETWEEN THE INTERNAL RESISTOR AND THE SENSOR CASE (GROUND). THIS CONDITION IS NOT CHECKED BY THE BULLETIN PROCEDURE.

WHEN USED TOGETHER WITH THE SERVICE MANUAL CODE 24 DIAGNOSTIC CHART, THE ABOVE PROCEDURE WILL DETECT A FAILED DISCRIMINATING SENSOR. PLEASE UPDATE YOUR SERVICE MANUALS TO REFLECT THIS ADDITIONAL CHECK.

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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.

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