Catalyst Monitor

OBD System Description - Catalyst Monitor

System Description / Monitoring Procedure
ECM calculates the oxygen storage capacity of TWC and monitors the ability of TWC to convert the exhaust emission effectively.
ECM calculates the oxygen storage capacity under specified driving conditions as follows.
1) ECM commands the fuel status to rich (air/fuel ratio: low) until all oxygen is released from
the TWC.
2) ECM commands the fuel status to lean (air/fuel ratio: high) until any one of the following
conditions is met, and ECM calculates the oxygen storage capacity of TWC by HO2S-2
sensor output signal and duration.
- Saturation of oxygen in the TWC is detected by output signal of HO2S-2.
- Before the saturation of oxygen is detected, the lean status of the fuel injection is longer than specified time. (ECM judges that the oxygen storage is higher than specified value.)

Catalyst System Layout
The system has HO2S located upstream and downstream of the TWC on each bank. The layout of TWC and HO2S is described below.

TWC, HO2S-1 and HO2S-2 layout






DTC Description / Detecting Condition / Confirmation Procedure
P0420 / P0430
Refer to DTC P0420 / P0430 P0420

Catalyst Monitor

Operation









Enable conditions






Typical malfunction thresholds






Mode $06 data