Catalytic Converter: Testing and Inspection

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 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.

ON-BOARD DIAGNOSIS LOGIC
OVERALL FUNCTION CHECK
Use these procedures to check the overall function of the three way catalyst. During these checks, a DTC might not be confirmed.




1) Start engine and warm it up sufficiently.
2) Set "MANU TRIG" and "HI SPEED", then select "FR O2 SEN-B1", "FR O2 SEN-B2", "RR O2 SEN-B1 or -B2", "FR O2 MNTR-B2", "FR O2 MNTR-B1", "RR O2 MNTR" in "DATA MONITOR" mode with CONSULT.
3) Touch "RECORD" on CONSULT screen with engine speed held at 2,000 rpm constant under no load.
4) Make sure that the switching frequency between "RICH" and "LEAN" of "RR O2 SEN-B1 or SEN-B2" is very less than that of "FR O2 SEN-B1" or "FR O2 SEN-B2".

Switching frequency ratio =
Rear heated oxygen sensor switching frequency / Front heated oxygen sensor switching frequency

This ratio should be less than 0.7.

If the ratio is greater than above, the three way catalyst is not operating properly.

NOTE:
- If the "FR O2 MNTR-B1" or "FR O2 MNTR-B2" does not indicate "RICH" and "LEAN" periodically more than 5 times within 10 seconds at step 3, perform TROUBLE DIAGNOSIS FOR DTC 0503 or 0303 first.

OR




1) Start engine and warm it up sufficiently.
2) Set voltmeters probes between ECM terminals (50) (front heated oxygen sensor (left bank) signal, (51) front heated oxygen sensor (right bank) signal and (25) (engine ground), and ECM terminals (56), (57) rear heated oxygen sensor signal (left and right) and (25) (engine ground).
3) Keep engine speed at 2,000 rpm constant under no load.
4) Make sure that the voltage switching.frequency (high & low) between ECM terminals (56) and (25) is very less than that of ECM terminals (50) and (25), or (51) and (25).

Switching frequency ratio =
Rear heated oxygen sensor voltage switching frequency / Front heated oxygen sensor voltage switching frequency

This ratio should be less than 0.7.

If the ratio is greater than above, it means three way catalyst does not operate properly.

NOTE:
- If the voltage at terminal (50) or (51) does not switch periodically more than 5 times within 10 seconds at step 3, perform TROUBLE DIAGNOSIS FOR DTC 0503 or 0303 first.

CATALYST FUNCTION DIAGNOSTIC PROCEDURE

Diagnostic Chart: