Troubleshooting

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

CIRCUIT DESCRIPTION

DTC Detection Condition:

The ECM observes the waveform of the heated oxygen sensor located behind the catalyst to determine whether the catalyst is performance has deteriorated.

If the catalyst is functioning normally, the waveform of the heated oxygen sensor located behind the catalyst switches back and forth between rich and lean much more slowly.

When the waveform of the heated oxygen sensor located behind the catalyst alternates flatteringly between rich and lean, it indicates that the catalyst performance has deteriorated.

CONFIRMATION ENGINE RACING PATTERN




1. Connect the OBD II scan tool or hand-held tester to the DLC3.
2. Stan engine and warm it up with all the accessories switched OFF until engine coolant temperature is stable.
3. Race the engine at 2,500 - 3,000 rpm for about 3 minutes.
4. When racing the engine at 3,000 rpm for 2 sec. and 2,000 rpm for 2 sec. alternately, check the waveform of the heated oxygen sensor (bank 1 sensor 2).

Step 1 - 2:

Step 3 - 4:

INSPECTION PROCEDURE

HINT: Read freeze frame data using hand-held tester or OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.