J30t V6-2960cc 3.0L DOHC MFI (VG30DE) (1997)
/Page-621001.png)
Catalytic Converter: Description and Operation
ON-BOARD DIAGNOSIS LOGIC
The ECM monitors the switching frequency ratio of front and rear heated oxygen sensors. A three way catalyst with high oxygen storage capacity
will indicate a low switching frequency of rear heated oxygen sensor. As oxygen storage capacity decreases, the rear heated oxygen sensor
switching frequency will increase. When the frequency ratio of front and rear heated oxygen sensors approaches a specified limit value, the second
stage diagnosis is applied. The second stage diagnosis switches the mixture ratio feedback control using front heated oxygen sensor to rear heated
oxygen sensor. Then the ECM measures the switching lag time between front and rear heated oxygen sensors. The longer lag time indicates the
greater oxygen storage capacity. If the lag time is within the specified level, the three way catalyst malfunction is diagnosed.