DTC P0420: Catalyst System Efficiency Below Threshold

WARNING: This page is about a different car, the 2004 Mazda RX-8. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: DTC P0420 Detection Condition & Possible Causes Chart

Courtesy of MAZDA MOTORS CORP.

Diagnostic Procedure

Fig 2: DTC P0420 Diagnostic Procedure Chart (Step 1-3)

Courtesy of MAZDA MOTORS CORP.

Fig 3: DTC P0420 Diagnostic Procedure Chart (Step 4-11)

Courtesy of MAZDA MOTORS CORP.