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 P0420CIRCUIT/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.
- Inspect for the following conditions, which may cause a diesel oxidation converter (DOC) to degrade:
- Off Road Fuel or Red Dye Fuel
- Low quality B-20 fuel
- Fuel Containing high sulfur content
- Engine oil or coolant consumption
- Leaking fuel injectors
- Inspect the DOC for the following conditions:
- Physical damage or alterations
- Internal rattles caused by a damaged catalyst substrate
- Exhaust leaks before or after the DOC.
- If a condition is found, replace the DOC.
- If all exhaust system inspections are normal, replace the DOC.
IMPORTANT:
Perform the Repair Verification after completing the Circuit/System Testing.
RENDER: 1.0x
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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.