P0420
DTC PO420 - Catalyst System Efficiency Below ThresholdCIRCUIT 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
USA and Canadian vehicles light up the MIL when a malfunction is detected.
SYSTEM CHECK DRIVING PATTERN
1. Connect the OBD-II scan tool Toyota hand-held tester to the DLC3.
2. Start and warm up the engine with all accessories switched OFF.
3. Drive the vehicle at 50 - 65 km/h (31 - 40 mph) for 5 - 10 min.
HINT: If a malfunction exists, the MIL will light up during step 3.
INSPECTION PROCEDURE
