DTC 0702

ON BOARD DIAGNOSIS LOGIC
The ECM monitors the switching frequency ratio of front heated oxygen sensor and rear heated oxygen sensor.
A warm-up 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 heated oxygen sensor and rear heated oxygen sensor approaches a specified limit value the warm-up three way catalyst malfunction is diagnosed.




DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE

OVERALL FUNCTION CHECK
Use this procedure to check the overall function of the warm-up 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 SENSOR", "RR O2 SENSOR", "FR O2 MNTR", "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 SENSOR".

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 0.7 the warm-up three way catalyst is not operating properly.

OR

WITHOUT SCAN TOOLS
(1) Start engine and warm it up sufficiently.




(2) Set voltmeter probes between ECM terminals (46) (front heated oxygen sensor signal) and (43) (engine ground), and ECM terminals (52) (rear heated oxygen sensor signal) and (43) (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 (52) and (43) is very less than that of ECM terminals (46) and (43).

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 0.7, it means warm-up three way catalyst does not operate properly.

NOTE: If the voltage at terminal (46) does not switch periodically more than 5 times within 10 seconds at step 3, perform TROUBLE DIAGNOSIS FOR DTC P0130 (Front heated oxygen sensor) first.




DIAGNOSTIC PROCEDURE