P0420

DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD





SYSTEM DIAGRAM

CIRCUIT DESCRIPTION
Exhaust oxygen concentration at the upper part and the lower part of TWC is detected from HO2S-1 and HO2S-2 respectively and accordingly ECM controls the closed loop which then controls the fuel injection volume. While the above control is going on and if TWC is in good condition, the output voltage of HO2S-2 is maintained at specified level. As TWC becomes deteriorated, even when the above control is going on, the exhaust gas which has passed TWC then passes HO2S-2 at the exhaust oxygen concentration similar to that of the upper part of TWC without being oxygenated or converted. Thus, waveforms of HO2S-1 and HO2S-2 output voltages become alike. ECM judges deterioration of TWC by comparing waveforms of HO2S-1 and HO2S-2.





DETECTING CONDITION





DTC CONFIRMATION PROCEDURE

WARNING:
- When performing a road test, select a place where there is no traffic or possibility of a traffic accident and be very careful during testing to avoid occurrence of an accident.
- Road test should be carried out with 2 persons, a driver and a tester, on a level road.

NOTE: Check to make sure that following conditions are satisfied when using this DTC CONFIRMATION PROCEDURE.
- Intake air temp. or intake air temp. at start: higher than -7°C (19°F)
- Engine coolant temp. at start: higher than -7°C (19°F)
- Atmospheric pressure: higher than 570 mmHg (Altitude: lower than 2360 m (7740 ft))





TROUBLESHOOTING