Diagnosis & Repair
- Connect scan tester. See Figure. Start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 5-10 minutes. Stop vehicle. Retrieve codes. See SELF-DIAGNOSTIC SYSTEM .
- If codes other than P0420 are present, diagnose and repair those codes first. If DTC P0420 is only displayed, inspect oxygen sensor circuits. See DTC P0130 - HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test. Repair as necessary. If oxygen sensor circuits and sensor are okay, replace catalytic converter and retest.