Catalytic Converter: Testing and Inspection

NOTE: Make sure that no HO2S DTC has been detected. If detected, this inspection cannot be used for TWC or WU-TWC inspection.

1. Connect the NGS tester and monitor PIDs as follows.
- California emission regulation applicable models
- Monitor the WU-TWC using FHO2S PID for upstream HO2S and RHO2S PID for downstream HO2S.
- Federal emission regulation applicable models
- Monitor TWC using FHO2S PID for upstream HO2S and RHO2S PID for downstream HO2S.

2. Press START to begin monitoring the appropriate PIDs.
3. Drive the vehicle for 10 minutes at 65 - 96 km/h {40 - 60 mph} to ensure the front catalytic converter reaches operating temperature.
4. Stop the vehicle and leave in a safe place.
5. Let the engine idle.
6. Press TRIGGER to begin recording PIDs.
7. Wait for 1 minute then press TRIGGER again to finish recording.
8. Select the appropriate PIDs and read the graph of "VIEW RECORDING".
9. Count the number of times (inversions) that the upstream HO2S graph line actually crosses the 0.5 V line.
10. Count the number of times (inversion) that the downstream HO2S graph line actually crosses the 0.5 V line.






NOTE: Do not count the number of peaks. Refer to the illustration.


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

Upstream HO2S Graph Line Example:

Downstream HO2S Graph Line Example 1:

Equation
RATIO = Upstream HO2S inversion + downstream HO2S Inversion

- If the ratio is 2 or more or no downstream HO2S inversion, the TWC or WU-TWC is functioning properly.
- If the ratio is less than 2, the TWC or WU-TWC is not functioning properly. Replace the TWC or WU-TWC.

Downstream HO2S Graph Line Example 2:

Equation
RATIO = 26 Inversions (upstream HO2S Inversions) + 7 Inversions (downstream HO2S Inversions) = 3.7 (good converter)

Downstream HO2S Graph Line Example 3:

Equation
RATIO = 26 Inversions (upstream HO2S Inversions) + 19 Inversions (downstream HO2S inversions) = 1.4 (bad converter)