OBD System Description - Catalyst Monitor (EVAP Leak Check Model)

OBD System Description - Catalyst Monitor (EVAP Leak Check Model)

System Description / Monitoring Procedure
Exhaust oxygen concentration at the upstream and the downstream of WU-TWC is detected from A/F sensor and HO2S respectively and accordingly ECM controls the closed loop which then controls the fuel injection volume. While the above controls is going on and if WU-TWC is in good condition, the output voltage of HO2S is maintained at specified level. As WU-TWC becomes deteriorated, even when the above control is going on, the exhaust gas which has passed WU-TWC then passes HO2S at the exhaust oxygen concentration similar to that of the upstream of WU-TWC without being oxygenated or converted. Thus, waveforms of A/F sensor and HO2S output voltage become alike, ECM judges deterioration of WU-TWC by comparing waveforms of A/F sensor and HO2S.

Catalyst System Layout
The system has A/F sensor and HO2S located upstream and downstream of WU-TWC as shown in figure.

WU-TWC, A/F sensor and HO2S layout






DTC Description / Detecting Condition / Confirmation Procedure
P0420
Refer to DTC P0420. P0420

Catalyst Monitor
















MODE $06 Data