DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD Toyota Prius I рестайлинг

Circuit Description

ECM compares waveform pattern of heated oxygen sensor No. 1 on exhaust pipe in front of catalytic converter with waveform pattern of heated oxygen sensor No. 2 on exhaust pipe behind catalytic converter to determine if catalytic converter performance has deteriorated. Air/fuel ratio compensation keeps the waveform pattern of heated oxygen sensor No. 1 repeatedly switching back and forth from rich to lean. If catalytic converter is functioning properly, the waveform pattern for heated oxygen sensor No. 2 should switch back and forth from rich to lean more slowly than heated oxygen sensor No. 1. If both waveform patterns switch at a similar rate, catalytic converter performance has deteriorated. DTC is set when both oxygen sensors have nearly the same waveform pattern after engine and catalytic converter are at normal operating temperature and vehicle is driven at 55 MPH for at least 5 minutes. Possible causes are

1. Exhaust system leak.
2. Defective heated oxygen sensor.
3. Defective catalytic converter.

Diagnostic Aids

Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.

If oscilloscope is available, switching rate of heated oxygen sensors may be checked by reading both heated oxygen sensor waveform patterns by connecting oscilloscope between terminals No. 17 (Brown wire) at ECM electrical connector E8 and No. 12 (White wire) for heated oxygen sensor No. 1, or No. 11 (Yellow wire) for heated oxygen sensor No. 2 at ECM electrical connector E10. This is the E1, OX1 and OX2 terminals on ECM. ECM is located behind the glove box. see scheme 3 For ECM electrical connector terminal identification see scheme 7 Start engine and warm engine to normal operating temperature. Ensure all accessories are off. Drive vehicle at 55 MPH for at least 5 minutes. Read heated oxygen sensor No. 1 waveform pattern and ensure waveform pattern oscillates around.5 volt. (Scheme 317) After reading heated oxygen sensor No. 1 waveform pattern, read heated oxygen sensor No. 2 waveform pattern. Heated oxygen sensor No. 2 waveform pattern should be a smooth line ranging from.6-.7 volt. If malfunction exists, the waveform pattern will be as displayed. (Scheme 317)

Scheme 317

1. Using Toyota hand-held tester or scan tool, check for any other DTCs. If only DTC P0420 exists, go to next step. If other DTCs exist, diagnose and repair those DTCs first and then retest.
2. Check exhaust system for leaks. If no exhaust leak exists, go to next step. If exhaust leak exists, repair exhaust system as necessary.
3. Check heated oxygen sensor No. 1. See «DTC P0130: HEATED OXYGEN SENSOR NO. 1 CIRCUIT»(ref-97394-S09671178082001050400000) . If heated oxygen sensor No. 1 operates properly, go to next step. If heated oxygen sensor No. 1 does not operate properly, repair or replace components as necessary.
4. Check heated oxygen sensor No. 2. See «DTC P0136: HEATED OXYGEN SENSOR NO. 2 CIRCUIT»(ref-97394-S02442270232001050400000) test. If heated oxygen sensor No. 2 operates properly, replace catalytic converter. If heated oxygen sensor No. 2 does not operate properly, repair or replace components as necessary.