DTC 0702

ON BOARD DIAGNOSIS LOGIC
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 three way catalyst malfunction is diagnosed.

OVERALL FUNCTION CHECK
Use this procedure to check the overall function of the three way catalyst. During this check, a 1st trip DTC might not be confirmed.

With Consult
(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 SENSOR", "FR 02 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 SENSOR" 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 1/2.

If the ratio is greater than 0.5, 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 P0130 or P0150 first.
Without Consult
(1) Start engine and warm it up sufficiently.




(2) Set voltmeters probes between ECM terminals (50) [front heated oxygen sensor (right bank) signal], (51) [front heated oxygen sensor (left bank signal and (25) (engine ground), and ECM terminals (rear heated oxygen sensor signal) 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 112.

If the ratio is greater than 0.5, 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.




DIAGNOSTIC PROCEDURE