Warm-Up Three-Way Catalytic Converter (WU-TWC) Inspection

WARNING: This page is about a different car, the 2005 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

Make sure that no HO2S DTCs have been detected. If detected, this inspection is not applicable for TWC inspection.

Connect the WDS or equivalent and monitor PIDs as following.
- Monitor the left WU-TWC using O2S21 PID for upstream HO2S and O2S22 PID for downstream HO2S.
- Monitor the right WU-TWC using O2S11 PID for upstream HO2S and O2S12 PID for downstream HO2S.
Begin to monitor the appropriate PIDs.
Drive the vehicle for 10 min at 65-96 km/h {40-60 mph} to allow the front catalytic converter to reach operating temperature.
Stop the vehicle and leave it in a safe place.
Let the engine idle.
Record PIDs for 1 min.
Select the appropriate PIDs and read the graph.
Count the number of times (inversions) that the upstream HO2S graph line actually crosses the 0.5 V line.

Fig 1: Upstream HO2S Graph Line
Courtesy of MAZDA MOTORS CORP.
Count the number of times (inversions) that the downstream HO2S graph line actually crosses the 0.5 V line.
NOTE:
- Do not count the number of peaks. Refer to the graph.
Using the following equation, calculate the value of ratio.
Equation
1. RATIO = Upstream HO2S inversion /downstream HO2S inversion
- If the ratio is 2 or more or there is no downstream HO2S inversion, the WU-TWC is functioning properly.
- If the ratio is less than 2 , the WU-TWC is not functioning properly. Replace the WU-TWC.
Upstream HO2S graph line example

Fig 2: Upstream HO2S Graph Line Example
Courtesy of MAZDA MOTORS CORP.

Downstream HO2S graph line example 1

Equation
1. RATIO = 26 inversions (upstream HO2S inversions) /7 inversions (downstream HO2S inversions) = 3.7 (good WU-TWC)
Fig 3: Downstream HO2S Graph Line Example 1
Courtesy of MAZDA MOTORS CORP.

Downstream HO2S graph line example 2

Fig 4: Downstream HO2S Graph Line Example 2
Courtesy of MAZDA MOTORS CORP.

Downstream HO2S graph line example 3

Equation
1. RATIO = 26 inversions (upstream HO2S inversions) /19 inversions (downstream HO2S inversions) = 1.4 (deteriorated WU-TWC)
Fig 5: Downstream HO2S Graph Line Example 3
Courtesy of MAZDA MOTORS CORP.