(g) Three-Way Catalyst Oxygen Storage Capacity

(g) Three-Way Catalyst Oxygen Storage Capacity




The control module monitors the post catalyst HO2S signal voltage in order to measure the oxygen storage capacity of the converter. A good catalytic converter is indicated when the post-catalyst HO2S signal voltage is relatively steady (2) compared to the pre-catalyst HO2S signal voltage (1).




A malfunctioning catalytic converter is indicated when the post-catalyst HO2S signal voltage is more active (2)~ similar to the pre-catalyst HO2S signal voltage (1).

In addition to catalyst monitoring the post catalyst HO2S has a limited role in fuel control.

IMPORTANT: Do not use post-catalyst HO2S voltage activity in order to determine the efficiency of the TWC converter unless directed to do so by a diagnostic procedure.

The catalyst monitor on-board diagnostic tests can be effected by the following:
- A slightly degraded or marginal catalyst
- Fuel containing high amounts of the following contaminants:
- Sulfur
- Silica
- Lead
- Phosphorus

- Exhaust system leaks may cause the following:
- Prevent a degraded or marginal TWC converter from failing a diagnostic test
- Cause a normally functioning TWC converter to fail a diagnostic test
- Prevent the diagnostic test from running

- An aftermarket HO2S
- An aftermarket catalytic converter