P0420

On Board diagnosis Logic
The ECM monitors the switching frequency ratio of heated oxygen sensor 1 (front) and 2 (rear).

A three way catalyst (manifold) 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 sensor 1 (front) and 2 (rear) approaches a specified limit value, the three way catalyst (manifold) malfunction is diagnosed.

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. 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 2,000 to 3,000 rpm and hold 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 until "INCMP" of "CATALYST" changes to "CMPLT" (It will take approximately 5 minutes.)

If not "CMPLT", stop engine and cool down to less than 70 °C (158 °F) and then retest from step 1.




7. Select "SELF-DIAG RESULTS" mode with CONSULT-II.




8. Confirm that the 1st trip DTC is not detected. If the 1st trip DTC is detected, go to "Diagnostic Procedure" below.

Overall Function Check
Use this procedure to check the overall function of the three way catalyst (manifold). During this check, a 1st trip DTC might not be confirmed.

CAUTION: Always drive vehicle at a safe speed.




With GST
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 terminal 50 [Heated oxygen sensor 1 (front) signal] and engine ground, and ECM terminal 56 [Heated oxygen sensor 2 (rear) 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 very 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 (manifold) does not operate properly. Go to "Diagnostic Procedure" below.

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

Diagnostic Procedure

Step 1:

Steps 2 - 4:

Steps 5 - 7:

Steps 8 - 9: