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 15 (BODY CONTROL MODULES)SELF-DIAGNOSTIC SYSTEMLIGHTING SYSTEM DIAGNOSTIC SYSTEM CHECK
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Lighting System Diagnostic System Check
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Lighting System Diagnostic System Check
WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, 2001 Chevrolet Monte Carlo, and 2001 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Use this check as starting point for any lighting system complaint.
- Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to RUN position. If scan tool powers up, go to next step. If scan tool does not power up, go to TEST D: SCAN TOOL DOES NOT POWER UP under SYSTEM TESTS.
- Turn ignition switch to RUN position. Using scan tool, attempt to establish communications with Driver Information Center (DIC). If communication is established, go to next step. If communication cannot be established, go to TEST C: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS.
- Select DISPLAY DTC function for BCM. Record all displayed DTCs and status of displayed DTCs. If any DTCs are displayed, go to next step. If no DTCs are displayed, attempt to diagnose suspect system. Go to appropriate system check for suspect system. See SYSTEM TESTS .
- Using scan tool, retrieve DTCs. If DTCs U1000-U1305 are not present, go to next step. If DTCs U1000-U1305 are present, go to TEST C: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS.
- Check for DTC B1000. If DTC is not present, go to next step. If DTC B1000 is present, go to DTC B1000: CONTROL MODULE MALFUNCTION under DIAGNOSTIC TESTS.
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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.