Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 117 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P1640: CONTROL MODULE OUTPUT CIRCUITDIAGNOSTIC PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Diagnostic Procedure
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTC P0753, P0758 or P1860 is also set, diagnose that DTC first. P1640 will also set if a 1-2 or 2-3 shift solenoid or TCC solenoid fault exists. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
- Turn ignition ON, engine OFF. Using scan tool, review DTC P1640 failure record. Observe A/C RELAY CKT OPEN SHORT TO GND. If scan tool reads YES, see DTC P1640: A/C RELAY CONTROL CIRCUIT LOW VOLTAGE . If scan tool reads NO, go to next step.
- Using scan tool, observe A/C RELAY CKT SHORT TO VOLTS. If scan tool reads YES, see DTC P1640: A/C RELAY CONTROL CIRCUIT HIGH VOLTAGE . If scan tool reads NO, go to next step.
- Using scan tool, observe MODULE DRIVER OVERVOLT and MODULE DRIVER OVERTEMP. If scan tool reads YES for either, record all PCM DTCs and reprogram PCM. See PCM REPROGRAMMING under PROGRAMMING. If this fault returns, replace and reprogram the PCM. If scan tool reads NO for both, see DIAGNOSTIC AIDS .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.