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 MANUALSPONTIAC2008GRAND PRIX BASEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 450 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 5.3L - DTC P0420 TO DTC P3449)DTC P0420REPAIR PROCEDURES
2008 Pontiac Grand Prix Base
Repair Procedures
2008 Pontiac Grand Prix BaseSECTION Repair Procedures
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.
IMPORTANT:
A new converter with less than 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
- Exhaust Leakage
- Exhaust Manifold Replacement - Left Side (3.8L) or Exhaust Manifold Replacement - Left Side (RPO LY7)
- Exhaust Manifold Replacement - Right Side (3.8L) or Exhaust Manifold Replacement - Right Side (RPO LY7)
- Heated Oxygen Sensor Replacement - Bank 1 Sensor 1
- Heated Oxygen Sensor Replacement - Bank 1 Sensor 2
- Restricted Exhaust
RENDER: 1.0x
NO RELATED
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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.