Three-Way Catalytic Converter (TWC) Inspection: Notes

WARNING: This page is about a different car, the 2004 Mazda 6. 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 the following PIDs.
- Monitor the right 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.
Idle the engine.
Record PIDs for 1 min.

Fig 1: Inversion Graph (Example)
Courtesy of MAZDA MOTORS CORP.
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.
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

RATIO = Upstream HO2S inversion / downstream HO2S inversion

If the ratio is 1.5 or more, or there is no downstream HO2S inversion, the TWC is functioning properly.
If the ratio is less than 1.5 , the TWC is not functioning properly. Replace the TWC.