Code 72

Three Way Catalyst Function Test:

Three Way Catalyst Function Test - CONSULT:

Instead of performing DTC DETECTING CONDITION, the following method can be used for checking the three way catalyst function. (The "NG" of the OVERALL FUNCTION CHECK means the same as the DTC detection.)

THREE WAY CATALYST FUNCTION (DTC: P0420)
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 1/2 (0.5) or less than that of "FR O2 SENSOR".

SWITCHING FREQUENCY RATIO
The switching frequency ratio = Rear heated oxygen sensor switching frequency divided by Front heated oxygen sensor switching frequency. This ratio should be less than 1/2 (0.5).
If the ratio is greater than 1/2 (0.5), the three way catalyst is not operating properly.

EXAMPLE: Rear O2 sensor is switching 5 times in 10 seconds.
Front O2 sensor is switching 10 times in 10 seconds.
5 divided by 10 = 0.5 Catalyst is GOOD.

Note: If the "FR O2 MNTR" does not indicate "RICH" and "LEAN" periodically more than 5 times for 10 seconds at step 3, perform TROUBLE DIAGNOSIS FOR DTC 33 (Front heated oxygen sensor) first.