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 1401 (LIGHTING SYSTEMS)DIAGNOSTIC INFORMATION AND PROCEDURESHEADLAMP SWITCH ON INDICATOR ALWAYS ON
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Headlamp Switch On Indicator Always On
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Headlamp Switch On Indicator Always On
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Headlamp Switch On Indicator Always On Diagnostic Test
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Interior Lights Dimming Schematics Connector End View Reference: Lighting Systems Connector End Views or Body Control System Connector End Views in Body Control System |
|||
| 1 | Did you perform the Lighting Systems Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Lighting Systems |
| 2 | Verify that the headlamp switch on indicator is always ON. Does the headlamp switch on indicator operate properly? |
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
| 3 | Are the headlamps operating properly? | Go to Step 4 | Go to Symptoms - Lighting Systems |
| 4 |
|
Go to Step 5 | Go to Step 6 |
| 5 | Test the headlamp on indicator control circuit for a short to ground. Refer to Circuit Testing
and Wiring Repairs
in Wiring Systems. Did you find and correct a condition? |
Go to Step 10 | Go to Step 7 |
| 6 | Inspect for poor connections at the harness connector of the headlamp switch. Refer to Circuit Testing
and Wiring Repairs
in Wiring Systems. Did you find and correct the condition? |
Go to Step 10 | Go to Step 8 |
| 7 | Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Circuit Testing
andWiring Repairs
in Wiring Systems. Did you find and correct the condition? |
Go to Step 10 | Go to Step 9 |
| 8 | Replace the headlamp switch. Refer to Headlamp Switch Replacement . Did you complete the repair? |
Go to Step 10 | - |
| 9 |
IMPORTANT:
Perform the setup procedure for the BCM. Replace the BCM. Refer to Body Control Module Replacement
in Body Control System.Did you complete the replacement? |
Go to Step 10 | - |
| 10 | Operate the system in order to verify the repair. Did you correct the condition? |
System OK | Go to Step 3 |
RENDER: 1.0x
NO RELATED
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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.