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.


DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE

CAUTION:
- Always drive vehicle at a safe speed.
- If "DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE" has been previously conducted, always turn ignition switch "OFF" and wait at least 5 seconds before conducting the next test.


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






Without TOOLS
(1) Start engine and warm it up to normal operating temperature.
(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) (ECM ground), and ECM terminals (56) (rear heated oxygen sensor signal) and (25) (ECM 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 switching frequency
----------------------------------------------
Front heated oxygen sensor switching frequency


This ratio should be less than 0.5.
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 P0130 or P0150 (0503 or 0303) first.

1 Of 2:

2 Of 2:

DIAGNOSTIC PROCEDURE