Warm Up Three-Way Catalytic Converter: Inspection

NOTE: Ensure no HO2S DTC has been detected. If detected, this inspection cannot be used.

1. Using scan tool, access O2S11 (front HO2S) and O2S12 (rear HO2S) PIDs.
2. Monitor appropriate PIDs.
3. Drive vehicle for 10 minutes at 40-60 MPH to ensure Warm Up Three-Way Catalytic Converter (WU-TWC) reaches operating temperature.
4. Stop vehicle, let engine idle and record PIDs for one minute.
5. Select appropriate PIDs and read graph. See Fig 1 or Fig 2 .
6. Count number of times graphline actually crosses .5V line (inversion) for both front and rear HO2Ss.
7. Divide number of front HO2S inversions by number of rear HO2S inversions for ratio data.
   • If ratio is 2 (1.5 on Mazda6) or more or no rear HO2S inversions, WU-TWC converter is functioning properly.
   • If ratio is less than 2 (1.5 on Mazda6), WU-TWC converter has deteriorated. See Fig 3. Replace faulty WU-TWC converter.

Fig 1: Identifying Front HO2S Graphline - Example

Courtesy of MAZDA MOTORS CORP.

Fig 2: Identifying Rear HO2S Graphlines - Examples For Properly Functioning WU-TWC Converter

Courtesy of MAZDA MOTORS CORP.

Fig 3: Identifying Rear HO2S Graphline - Example For Deteriorated WU-TWC Converter

Courtesy of MAZDA MOTORS CORP.