P0420

On Board Diagnosis Logic
The 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.

*: Warm-up three way catalyst (For California)

DTC Confirmation Procedure

NOTE: If "DTC Confirmation Procedure" has been previously conducted, always turn ignition switch OFF and wait at least 5 seconds before conducting the next test.

With CONSULT-II
1. Start engine and drive vehicle at a speed of more than 70 km/h (43 MPH) for 2 consecutive minutes.
2. Stop vehicle with engine running.




3. 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-II.
4. Touch "RECORD" on CONSULT-II screen with engine speed held at 2,000 rpm constantly under no load.
5. Make sure that the switching frequency between "RICH" and "LEAN" of "RR O2 MNTR" is much less than that of "FR O2 MNTR" as shown below.
Switching frequency ratio = A/B
A: Rear heated oxygen sensor switching frequency
B: Front heated oxygen sensor switching frequency This ratio should be less than 0.75.
If the ratio is greater than above, the warm-up three way catalyst (models for California) is not operating properly.
If the "FR O2 MNTR" does not indicate "RICH" and "LEAN" periodically more than 5 times within 10 seconds at step 4, perform trouble diagnoses for DTC P0133 first.
If the result is NG, go to "Diagnostic Procedure" below. If the result is OK, go to following step.
6. Select "AUTO TRIG" in "DATA MONITOR" mode with CONSULT-II.




7. Drive vehicle (with transmission in 5th position) at a speed of approximately 84 to 96 km/h (52 to 60 MPH) with the following for at least 10 consecutive minutes.
(Drive the vehicle in an area where vehicle speed and accelerator pressure can be held steady and constant.)
If 1st trip DTC is detected, go to "Diagnostic Procedure" below.
8. Select "SRT STATUS" in "DTC CONFIRMATION" mode with CONSULT-II.
9. Verify that "CATALYST" is "CMPLT".
If not "CMPLT", repeat the test from step 6.

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.

Without CONSULT-II
1. Start engine and drive vehicle at a speed of more than 70 km/h (43 MPH) for 2 consecutive minutes.
2. Stop vehicle with engine running.




3. Set voltmeters probes between ECM terminals 50 (Front heated oxygen sensor signal), 56 (Rear heated oxygen sensor signal) and engine ground.
4. Keep engine speed at 2,000 rpm constant under no load.
5. Make sure that the voltage switching frequency (high & low) between ECM terminal 56 and engine ground is much less than that of ECM terminal 50 and engine ground.
Switching frequency ratio = A/B
A: Rear heated oxygen sensor voltage switching frequency
B: Front heated oxygen sensor voltage switching frequency
This ratio should be less than 0.75.
If the ratio is greater than above, it means three way catalyst does not operate properly.

NOTE: If the voltage at terminal 50 does not switch periodically more than 5 times within 10 seconds at step 4, perform trouble diagnosis for DTC P0133 first.

Diagnostic Procedure

Step 1 - 4:

Step 5 - 6:

Step 7 - 9: