Additional Inspections

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

Check the CKP sensor "B" for an internal short.
Check for proper Exhaust Gas Recirculation (EGR) system operation. Go to DTC P0401: EGR SYSTEM .
Inspect 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.