Bank 2

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 waveform change at a similar rate, it indicates that catalyst performance has deteriorated.




DETECTING CONDITIONS




CONFIRMATION ENGINE RACING PATTERN
1. Connect the TOYOTA hand-held tester to the DLC3, or connect the probe of the oscilloscope between terminals OXL1, OXL2, OXR1 OXR2 and E1 of the ECM connector.
2. Start the engine and warm it up with all accessories switched OFF until engine coolant temperature is stable.
3. Race the engine at 2,500 - 3,000 rpm for about 3 min.
4. After confirming that the waveform of the heated oxygen sensor (bank 1, 2 sensor 1 (OXL1, OXR1)), oscillate around 0.5 V during feedback to the ECM, check the waveform of the heated oxygen sensor (bank 1,2 sensor 2 (OXL2, OXR2)).






HINT: If there is a malfunction in the system, the waveform of the heated oxygen sensor (bank 1, 2 sensor 2 (OXL2, OXR2)) is almost the same as that of the heated oxygen sensor (bank 1, 2 sensor 1 (OXL1, OXR1)) on the left.
There are some cases where, even though a malfunction exists, the MIL may either light up or not light up.

Step 1:

Step 2:

Step 3:

Step 4:

INSPECTION PROCEDURE

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