P0420
DTC P0420 THREE WAY CATALYST FUNCTION
On Board Diagnosis Logic
The ECM monitors the switching frequency ratio of heated oxygen sensors 1 and 2.
A three way catalyst (manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.
When the frequency ratio of heated oxygen sensors 1 and 2 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 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. Start engine and warm it up to the normal operating temperature.
2. Turn ignition switch "OFF" and wait at least 10 seconds.
3. Start engine and keep the engine speed at between 3,500 to 4,000 rpm for at least one minute under no load.
4. Let engine idle for one minute.
5. Open engine hood.
6. Select "DTC & SRT CONFIRMATION" then "SRT WORK SUPPORT" mode with CONSULT-II.
7. Rev engine up to 2,000 to 3,000 rpm and hold it for 3 consecutive minutes then release the accelerator pedal completely. If "INCMP" of "CATALYST" changed to "COMPLT", go to step 10.
8. Wait 5 seconds at idle.
9. Rev engine up to 2,000 to 3,000 rpm and maintain it until "INCMP" of "CATALYST" changes to "CMPLT" (It will take approximately 5 minutes). If not "CMPLT", perform the following.
a. Turn ignition switch "OFF" and leave the vehicle in a cool place (soak the vehicle).
b. Turn ignition switch "ON" and select "COOLANTEMP/S" in "DATA MONITOR" mode with CONSULT-II.
c. Start engine and warm it up while monitoring "COOLANTEMP/S" indication on CONSULT-II.
d. When "COOLANTEMP/S" indication reaches to 70°C (158°F), go to step 3.
10. Select "SELF-DIAG RESULTS" mode with CONSULT-II.
11. 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 warm it up to the normal operating temperature.
2. Turn ignition switch "OFF" and wait at least 10 seconds.
3. Start engine and keep the engine speed at between 3,500 to 4,000 rpm for at least one minute under no load.
4. Let engine idle for one minute.
5. Set voltmeters probes between ECM terminals 91 [heated oxygen sensor 1 bank 1 signal], 92 [heated oxygen sensor 1 bank 2 signal] and engine ground, and ECM terminals 88 [heated oxygen sensor 2 bank 1 signal], 90 [heated oxygen sensor 2 bank 2 signal] and engine ground.
6. Keep engine speed at 2,000 rpm constant under no load.
7. Make sure that the voltage switching frequency (high & low) between ECM terminals 88 and engine ground, or 90 and engine ground is very less than that of ECM terminals 91 and engine ground, or 91 and engine ground.
Switching frequency ratio = A/B
A: Heated oxygen sensor 2 voltage switching frequency
B: Heated oxygen sensor 1 voltage switching frequency This ratio should be less than 0.75.
If the ratio is greater than above, it means warm-up three way catalyst does not operate properly. go to "Diagnostic Procedure" below.
NOTE: If the voltage at terminal 92 or 91 does not switch periodically more than 5 times within 10 seconds at step 5, perform trouble diagnosis for "DTC P0133, P0153 first".
Diagnostic Procedure
