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.
Repair Verification
2008 Pontiac Grand Prix BaseSECTION Repair Verification
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
- Clear the DTCs.
- Allow the engine coolant temperature to reach 70°C (156°F).
- Place the gear selector in Park for the automatic transmission or Neutral for the manual transmission.
- Set the parking brake.
- Press and hold the service brake.
- Run the engine for 6 minutes at 2,500 RPM.
- Allow engine speed to return to idle speed, then place gear selector into Drive for the automatic transmission, or apply clutch pedal for the manual transmission.
- After 2 minutes, verify that DTC P0420 has passed or failed this ignition cycle.
- If not passed or failed this ignition cycle, the test aborted resulting in an inconclusive test result. The above test may need to be repeated up to 5 more times during this drive cycle. The first test should be run after the initial warm-up period of 6 minutes. Between subsequent tests, maintain 2,500 RPM for 2 minutes.
- If 6 tests have been attempted and the DTC has not run or passed during this key cycle, turn the key to OFF for 30 seconds, then run the procedure a second time.
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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.