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 143 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)IGNITION SYSTEMIGNITION RELAY DIAGNOSIS (5.7L BI-FUEL)TEST DESCRIPTION
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Test Description
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Test Description
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2002 Saturn Vue, 2002 Pontiac Montana, 2002 Pontiac Aztek, 2002 Oldsmobile Silhouette, and 2002 Oldsmobile Bravada. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to step numbers in diagnostic procedure.
- 1
The System Check must be performed before proceeding with this diagnostic test. Failure to perform System Check will result in misdiagnosis. - 3
This step inspects Alternative Fuels Engine Control Module (AF ECM) fuses for opens and also tests voltage supply to fuses. - 5
This step inspects if AF ECM is powered-up. - 6
This step tests battery positive and switched ignition voltage circuits to AF ECM. - 7
This step tests AF ECM ground circuits. - 8
This step inspects for proper operation of fuel gauge select switch. If switch operates, then ignition relay is ON. - 11
This step inspects ignition relays ability to turn OFF. - 14
This step tests ignition relay coils ground circuit. If test light illuminates, then ignition relay must be faulty. - 15
This step indicates components or circuits that may have caused a fuse to open. Some components may require they be turned on in order to open fuse. An example would be depressing fuel gauge select switch in order to test select switch circuit for a short.
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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.