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 G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 2369 (ENGINE CONTROLS AND FUEL - 3.6L - DTC P0201 TO DTC P0629)DTC P0420 OR P0430CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6
Circuit/System Testing
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Circuit/System Testing
WARNING: This page is about a different car, the 2010 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
- Observe the DTC information with a scan tool. Verify there are no HO2S, fuel system, or misfire DTCs set.
- If there are any of the DTCs set, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC before proceeding with this diagnostic procedure.
- Verify the following conditions do not exist with the catalytic converter:
- Dents
- A severe discoloration caused by excessive temperatures
- Road damage
- An internal rattle caused by damaged catalyst substrate
- Restrictions
- If a condition is found, repair as necessary.
- Verify the following conditions do not exist with the exhaust system:
- Leaks
- Physical damage
- Loose or missing hardware
- Improperly torqued HO2S
- If a condition is found, repair the exhaust system.
- Verify the following conditions do not exist with the HO2S 2:
- A grounded wiring harness
- Damage
- If a condition is found, replace the HO2S 2.
- If no physical condition is detected and the HO2S 2 is as active as the HO2S 1 after operating the engine at 1,500 RPM for 1 minute and then returning to a stabilized idle, then replace the catalytic converter
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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.