Code 72

Three Way Catalyst Function Test:

3-way Catalyst Functional Test:

THREE WAY CATALYST FUNCTION (DTC: P0420)
1) Start engine and warm it up sufficiently.
2) Set voltmeters 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 46 and 43 is very less than that of ECM terminals 52 and 43.

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.