Monitoring Procedure

Primary detection is based upon;
1. Downstream O2 sensor high frequency amplitude.
2. The response delay time between upstream and downstream change.

A calculation of the average value of the downstream O2 sensor high frequency amplitude is made; this is normal if the value falls below a given threshold. Should a failure judgement occur, the main feedback frequency will be adjusted and the response delay time from the upstream to downstream feedback signal monitored. If the response delay time is greater than the threshold then a normal judgement will be made, less will incur a failure judgement.