P0420
ON BOARD DIAGNOSIS LOGIC
The ECM monitors the switching frequency ratio of front and rear heated oxygen sensors.
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)
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
Without Consult
Use this procedure to check the overall function of the three way catalyst.
During this check, a 1st trip DTC might not be confirmed.
1. Start engine and drive vehicle at a speed of more than 70 kph (43 mph) for 2 consecutive minutes.
2. Stop vehicle with engine running.
3. Set voltmeters probes between ECM terminals (46)(front heated oxygen sensor signal) and engine ground, and ECM terminals (52)(rear heated oxygen sensor 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 =
Rear heated oxygen sensor voltage switching frequency
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 (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
