Troubleshooting

DTC P0420 Catalyst System Efficiency Below Threshold

CIRCUIT DESCRIPTION





The ECM 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.





DETECTING CONDITION





SYSTEM CHECK DRIVING PATTERN
(1) Connect the OBD II scan tool or LEXUS hand-held tester to the
(2) Start and warm up the engine with all accessories switched OFF.
(3) Run the vehicle at 50 ~ 65 km/h (31 ~ 40 mph) for 5 ~ 10 mins.

HINT: If a malfunction exists, the MIL will light up during step (3).

Step 1:

Step 2:

Step 3:

INSPECTION PROCEDURE