DTC P0420: Catalytic System Efficiency Below Threshold

Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DTCS  . Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral, until radiator fan comes on. Allow engine to idle. Connect SCS service connector. Test drive vehicle at 40-55 MPH for approximately 2 minutes. Decelerate for at least 3 seconds with throttle fully closed. Reduce vehicle speed to 35 MPH, and hold it there until readiness code comes on. If DTC P0420 is not indicated, problem is intermittent, system is okay at this time. If DTC P0420 is indicated, inspect Warm-Up Three Way Catalytic Converter (TWC), if equipped and/or Three-Way Catalytic Converter (TWC) for plugging, melting, cracking, exhaust system leaks. Repair or replace as necessary.