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 CARSECTION 559 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 4.3L - DTC P0340 TO DTC P2138)DTC P0420 OR P0430REPAIR VERIFICATION
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Repair Verification
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Repair Verification
WARNING: This page is about a different car, the 2009 GMC Savana and 2009 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
- Verify that no other DTCs are set.
- If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
- Operate the vehicle within the Conditions for Running the DTC while observing the scan tool TWC Mon. OFF Idle Test Conditions Met parameter. The parameter will change to Yes when the OFF Idle Conditions have been met.
- If not the specified value, operate the vehicle within the OFF Idle Conditions.
- When the parameter has changed to Yes and the conditions are safe, stop and idle the vehicle in gear.
- Apply the service brake.
- Monitor the scan tool TWC Monitor Test State parameter. When the parameter indicates Active, the TWC Mon Test is running.
- Continue to monitor the parameter. When the parameter indicates Inactive, the TWC Mon Test has completed.
- When the test has completed, the TWC Monitor Test Count parameter will increment by one and the TWC Monitor Test Result parameter will indicate Pass, Fail, or No Decision.
- If no decision has been made, repeat steps 2-6 until the Test Result parameter indicates a Pass or Fail.
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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.