Catalytic Converter: Testing and Inspection

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

1. Connect the NGS tester and monitor PIDs as following.
- Monitor TWC using MHO2S 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 kph {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 at 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 H02S 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.

Equation: RATIO = Upstream HO2S inversion ÷ downstream HO2S Inversion

- 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 Graphline Example:

Downstream HO2S Graphline Example 1:

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

Downstream HO2S Graphline Example 2:

Downstream HO2S Graphline Example 3:

Equation: RATIO = 26 Inversions (upstream HO2S Inversions) ÷ 19 Inversions (downstream HO2S Inversions) = 1.4 (bad converter)