Description

DATA TROUBLE CODE: P0420

SYSTEM: Catalyst System Efficiency Below Threshold

CIRCUIT DESCRIPTION





The Engine Control Module compares the waveform of the Oxygen Sensor located before the catalyst with the waveform of the Oxygen Sensor located after the catalyst to determine whether or not catalyst performance has deteriorated.
Air-fuel ratio feedback compensation keeps the waveform of the Oxygen Sensor before the catalyst repeatedly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the Oxygen Sensor after the catalyst switches back and forth between rich and lean much more slowly than the waveform of the Oxygen Sensor before the catalyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.

DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
- After the engine is warmed up and the vehicle driven for 5 minutes at 32 to 80 km/h (20 to 50 mph), the waveforms of the Heated Oxygen Sensors. bank 1, 2 sensor 1 and bank 1 sensor 2 have the same amplitude.

TROUBLE AREA
- Three Way Catalytic Converter.
- Open or short in Heated Oxygen Sensor circuit.
- Heated Oxygen Sensor.

NOTE: Only on U.S. vehicles does the Malfunction Indcator Lamp light up when a malfunction is detected.

SYSTEM CHECK DRIVING PATTERN





1. Connect the OBDII scan tool or LEXUS hand-held tester to the Data Link Connector 3.
2. Start and warm up the engine with all accessories switched OFF.
3. After the engine is warmed up, run the vehicle at 50 to 65 km/h (31 to 40 mph) for 5 to 10 minutes.

NOTE: If a malfunction exists, the Malfunction Indcator Lamp will light up during step 3.