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.)