DTC P0420: Catalyst System Efficiency Below Threshold

NOTE: If DTCs P0137, P0138, and/or P0141 are indicated, trouble shoot DTC P0420 last.

NOTE: DTC P0420 is set and MIL illuminated when deterioration has been detected during 3 consecutive trips.

Perform PCM reset procedure. See POWERTRAIN CONTROL MODULE RESET PROCEDURE . Start engine. Hold engine speed at 3000 RPM under no load condition with transaxle in Neutral or Park until radiator fan comes on. Connect SCS service connector (07PAZ-0010100) to 2-pin service check connector located behind right side of center console. Test drive vehicle at 40-55 MPH for about 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 Three Way Catalytic Converter (TWC) for plugging, melting, cracking, or exhaust leaks. Repair or replace TWC as necessary. Perform final procedure. See FINAL PROCEDURE .