Additional Checks
- Check the Crankshaft Position (CKP) sensor "B" for an internal short.
- Check for proper Exhaust Gas Recirculation (EGR) system operation. See DTC P0401: EGR FLOW INSUFFICIENT under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
- Check the transaxle range switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.
- Check the Torque Converter Clutch (TCC) operation. TCC applying too soon can cause the engine to spark knock.
- If the 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.