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 MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 12 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 6.6L (LMM) - DTC P0300 TO DTC P0699)DTC P0671-P0678CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different variant/trim than selected.
IMPORTANT:
If a glow plug is replaced and the tip is missing or burned off, the cylinder head must be removed and all debris be cleaned out of the cylinder.
- With the ignition ON and the glow plugs not commanded ON, probe the affected glow plug with a test lamp connected to ground. Observe that the test lamp does not illuminate.
- If the test lamp does illuminate, test the glow plug control circuit for a short to voltage or for a faulty glow plug control module (GPCM). Replace the affected glow plug after repair.
- With the ignition ON, probe the affected glow plug with a test lamp connected to ground. Command the glow plugs ON with a scan tool and observe the test lamp. The test lamp should illuminate.
- If the test lamp does not illuminate, test the affected glow plug harness between the glow plug control module and the glow plug for an open, short to ground or high resistance.
- With the ignition OFF and the affected glow plug disconnected, measure the resistance between the affected glow plug terminal A and ground with a DMM for less than 1 ohm.
- If the resistance is more than 1 ohm, replace the affected glow plug.
- With the ignition OFF and the glow plug control module harness disconnected, measure the resistance between the affected glow plug harness connector terminal A and the corresponding glow plug control module harness connector terminal for less than 1 ohm resistance.
- If the resistance is more than 1 ohm, repair the harness.
- If the resistance is less than 1 ohm, replace the glow plug control module.
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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.