Warm Up Three-Way Catalytic Converter: Inspection

Using scan tool, access O2S11 (front HO2S) and O2S12 (rear HO2S) PIDs. Drive vehicle for 10 minutes at 40-60 MPH to ensure Warm Up Three-Way Catalytic Converter (WU-TWC) reaches operating temperature. Let engine idle and record PIDs for one minute. Scan tool should display graphs for O2S11 and O2S12. See Fig 1 and Fig 2 . Count number of times graphline crosses below .5V line (inversion) for both front and rear HO2Ss. Divide number of inversions for front HO2S by number of inversions for rear HO2S for ratio data. If ratio is 2 or more or no rear HO2S inversions, WU-TWC converter is functioning properly. See Fig 1 and Fig 2 . If ratio is less than 2, WU-TWC converter has deteriorated. See Fig 1 and Fig 3 . Replace 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.