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## 2008 - MX-5 - Engine

### WARM-UP THREE-WAY CATALYTIC CONVERTER (WU-TWC) INSPECTION [LF]

NOTE:

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

1. Connect the M-MDS and monitor PIDs as following.
• Monitor the WU-TWC using O2S11 PID for upstream HO2S and O2S12 PID for downstream HO2S.

2. 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. Idle the engine.
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 1.5 or more or there is no downstream HO2S inversion, the WU-TWC is functioning properly.

• If the ratio is less than 1.5, the WU-TWC is not functioning properly. Replace the WU-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 WU-TWC)

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