P0420
DTC P0420The catalyst's efficiency is demonstrated by its ability to oxidize CO and hydrocarbon emissions. The ECM/PCM compares the output signals of the front and rear oxygen sensors to determine whether the output of the rear sensor is beginning to match the output of the front oxygen sensor. Air/fuel mixture compensation keeps the frequency of the front oxygen sensor high due to the changes from rich-to-lean combustion. The catalyst causes the rear oxygen sensor to have a lower frequency. As the catalyst wears, the rear oxygen sensor's signal trace begins to match the front oxygen sensor's signal trace. That is because the catalyst becomes saturated with oxygen and cannot use the oxygen to convert hydrocarbon and CO into H_O and CO_ with the same efficiency as when it was new. A completely worn catalyst shows a 100% match between the frequency of the front and rear sensors.
DTC DESCRIPTION
If amplitude of B1S2 is over 0.5 voltage during 60 sec under enable conditions, ECM/PCM sets DTC P0420.
DTC Detecting Condition:
MONITOR SCANTOOL DATA
1. Connect scantool to Data Link Connector(DLC).
2. Warm up the engine to normal operating temperature.
3. Monitor the "B1S1 and B1S2" parameters on the scantool.
YES - Fault is intermittent caused by poor contact in the sensor's and/or ECM's connector or was repaired and ECM/PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of vehicle Repair" procedure.
NO - Go to "System Inspection" procedure.
SYSTEM INSPECTION
1. Exhaust gas system check.
a. Visual check.
- Check air leakage at junction of HO2S or Catalyst converter.
- Check looseness, poor connection, or damage.
b. Is there something wrong?
YES - Repair as necessary and then, go to "Verification of Vehicle Repair" procedure.
NO - Go to "Component inspection" procedure.
COMPONENT INSPECTION
1. Rear HO2S(B1S2) check.
a. B1S2 visual check
- Check assembling state of B1S2. (Check the interference between sensor wiring and exhaust pipe.)
- Check corrosion, contamination, or damage on sensor terminal and connector.
b. Is there something wrong?
YES - Repair as necessary and then, go to "Verification of Vehicle Repair" procedure.
NO - Go to "Catalyst converter check" procedure.
2. Catalyst converter check.
a. Catalyst converter visual check.
- Check discoloration by over-heating.
- Check deflection or crack(hole).
- Check noise.
b. Check whether the catalyst converter is genuine.
c. Is there something wrong?
YES - Substitute with a known - good Catalyst Converter and check for proper operation. If the problem is corrected, replace Catalyst Converter and then go to "Verification of Vehicle Repair" procedure.
NO - Substitute with a known - good ECM/PCM and check for proper operation. If the problem is corrected, replace ECM/PCM and then go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.
2. Clear the DTCs and Operate the vehicle within DTC Enable conditions in General information.
3. Are any DTCs present ?
YES - Go to the applicable troubleshooting procedure.
NO - System is performing to specification at this time.