P0420

ON BOARD DIAGNOSES LOGIC
The ECM monitors the switching frequency ratio of heated oxygen sensors 1 (front) and 2 (rear).

Three way catalyst with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2 (rear). As oxygen storage capacity decreases, the heated oxygen sensor 2 (rear) switching frequency will increase.

When the frequency ratio of heated oxygen sensors 1 (front) and 2 (rear) approaches a specified limit value, the three way catalyst malfunction is diagnosed.







DIAGNOSTIC TROUBLE CODE 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.

TESTING CONDITION:
- Open engine hood before conducting following procedure.
- Do not hold engine speed more than specified minutes below.

With Consult
1. Turn ignition switch "ON".
2. Select "DTC & SRT CONFIRMATION" then "SRT WORK SUPPORT" mode with CONSULT-II.
3. Start engine.
4. Rev engine up to 2,500 to 3,500 rpm and hold it for 3 consecutive minutes then release the accelerator pedal completely.
If "INCMP" of "CATALYST" changes to "CMPLT", go to step 7.
5. Wait 5 seconds at idle.
6. Rev engine up to 2,000 to 3,000 rpm and hold it until "INCMP" of "CATALYST" changes to "CMPLT" (It will take maximum of approximately 5 minutes.)




7. Select "SELF-DIAG RESULTS" mode with CONSULT-II.
If the 1st trip DTC is detected, go to "Diagnostic Procedure" below. If not "CMPLT", stop engine and cool down "COOLANT TEMP/SE" to less than 70 °C (158 °F) and then retest from step 1).

OR




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
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 (46) [heated oxygen sensor 1 (front) signal] and engine ground, and ECM terminals (52) [heated oxygen sensor 2 (rear) signal] and 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 terminals (52) and ground is much less than that of ECM terminals (46) and (43).
Switching frequency ratio = Heated oxygen sensor 2 (rear) voltage switching frequency / Heated oxygen sensor 1 (front) 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 (46) does not switch periodically more than 5 times within 10 seconds at step 4, perform TROUBLE DIAGNOSIS FOR DTC P0133 first.

6. If NG, go to "Diagnostic Procedure" below.

DIAGNOSTIC PROCEDURE

Part 1:

Part 2: