P0420
On Board Diagnosis Logic
The ECM monitors the switching frequency ratio of sensor 1 and sensor 2 of heated oxygen sensors.
A 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 sensor 1 and sensor 2 heated oxygen sensors approaches a specified limit value, the three way catalyst malfunction is diagnosed.
DTC Confirmation Procedure
NOTE: If "DTC Confirmation Procedure" has been previously conducted, always turn ignition switch "OFF" and wait at least 10 seconds before conducting the next test.
WITH CONSULT-II
TESTING CONDITION:
- Open engine hood before conducting the following procedure.
- Do not hold engine speed for more than the specified minutes below.
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 3,000 ± 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 2,500 ± 500 rpm and maintain it until "INCMP" of CATALYST changes to "CMPLT" (It will take approximately 5 minutes).
If not "CMPLT", stop engine and cool it 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. During this check, a 1st trip DTC might not be confirmed.
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 terminals and engine ground as follows.
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 94 (95) and engine ground is much less than that of ECM terminal 62 (63) 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 62 (63) does not switch periodically more than 5 times within 10 seconds at step 4, perform trouble diagnosis for DTC P0133 first.
Diagnostic Procedure
Diagnostic Procedure Step 1:
Diagnostic Procedure Steps 2 - 5:
