Three-Way Catalytic Converter (TWC) Inspection

WARNING: This page is about a different car, the 2005 Mazda MX-5 Miata. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

Make sure that no HO2S DTC has been detected. If detected, this inspection cannot be used for TWC inspection.

Connect the WDS or equivalent and monitor PIDs as follows:
- Monitor TWC using O2S11 PID for upstream HO2S and O2S12 PID for downstream HO2S.
Begin monitoring the appropriate PIDs.
Drive the vehicle for 10 min at 65-96 km/h {40-60 mph} to ensure the front catalytic converter reaches operating temperature.
Stop the vehicle and leave in a safe place.
Idle the engine.
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.
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 Fig 1.
Using the following equation, calculate the value of ratio.
Equation

RATIO = Upstream HO2S inversion DIVISION downstream HO2S inversion

Fig 1: Identifying Upstream HO2S Graph Line
Courtesy of MAZDA MOTORS CORP.

If the ratio is 2 or more or no downstream HO2S inversion, the TWC is functioning properly.
If the ratio is less than 2 , the TWC is not functioning properly. Replace the TWC.
Upstream HO2S graph line example

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

Downstream HO2S graph line example 1

Fig 3: Identifying Good Catalytic Converter (7 Inversions) Graph
Courtesy of MAZDA MOTORS CORP.

Equation

RATIO = 26 inversions (upstream HO2S inversions) DIVISION 7 inversions (downstream HO2S inversions) = 3.7 (good converter)

Downstream HO2S graph line example 2

Fig 4: Identifying Good Catalytic Converter (No Inversions) Graph
Courtesy of MAZDA MOTORS CORP.

Downstream HO2S graph line example 3

Fig 5: Identifying Bad Catalytic Converter (19 Inversions) Graph
Courtesy of MAZDA MOTORS CORP.

Equation

RATIO = 26 inversions (upstream HO2S inversions) DIVISION 19 inversions (downstream HO2S inversions) = 1.4 (bad converter)