Troubleshooting

DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

CIRCUIT DESCRIPTION

DTC Detecting Condition:

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

CONFIRMATION ENGINE RACING PATTERN




a. Connect the OBD II scan tool or hand-held tester to the DLC3.
b. Start engine and warm it up with all the accessories switched OFF until the water temperature is stable.
c. Race the engine at 2,500 - 3,000 rpm for about 3 minutes.
d. When racing the engine at 3,000 rpm for 2 seconds and 2,000 rpm for 2 seconds 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 OBD II scan tool or hand-held tester. Because freeze frame records the engine conditions when the malfunction is detected. When troubleshooting, it is useful to determine 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.