Additional Checks
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
- Check for proper Exhaust Gas Recirculation (EGR) system operation. See DTC P0401: EGR SYSTEM INSUFFICIENT FLOW under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article.
- Inspect the Transaxle Range Switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.
- Check Torque Converter Clutch (TCC) operation. TCC applying too soon can cause the engine to spark knock. See appropriate DIAGNOSIS article in TRANSMISSIONS.
- If scan tool readings are normal and there are no engine mechanical faults, fill the fuel tank with a known quality gasoline that has a minimum octane reading of 87 and re-evaluate vehicle performance.