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)