Mazda 6 Service Manual: Three-way catalytic converter (twc) inspection

Note

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

1. Connect the WDS or equivalent and monitor PIDs as following.

• Monitor the right TWC using O2S11 PID for upstream HO2S and O2S12 PID for downstream HO2S.

2. Begin to monitor the appropriate PIDs.

3. Drive the vehicle for 10 min at 65-96 km/h {40-60 mph}

to allow the front catalytic converter to reach operating temperature.

4. Stop the vehicle and leave it in a safe place.

5. Let the engine idle.

6. Record PIDs for 1 min.

7. Select the appropriate PIDs and read the graph.

8. Count the number of times (inversions) that the upstream HO2S graph line actually crosses the 0.5 V

line.

9. 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.

10. Using the following equation, calculate the value of ratio.

Equation
RATIO = Upstream HO2S inversion ÷ downstream HO2S inversion

• If the ratio is 5.5

  or more or there is no downstream HO2S inversion, the TWC is functioning properly.

• If the ratio is less than 1.125,

  the TWC is not functioning properly. Replace the TWC.

Upstream HO2S graph line example

Downstream HO2S graph line example 1

Equation
RATIO = 30 inversions (upstream HO2S inversions) ÷ 5 inversions (downstream HO2S inversions) = 6.0 (good WU-TWC)

Downstream HO2S graph line example 2

Downstream HO2S graph line example 3

Equation
RATIO = 30 inversions (upstream HO2S inversions) ÷ 27 inversions (downstream HO2S inversions) = 1.1 (bad converter)