Catalyst Monitor
OBD System Description - Catalyst MonitorSystem Description / Monitoring Procedure
Exhaust oxygen concentration at the upper part and the lower part 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 upper part 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 4 oxygen sensors located upstream and downstream of the catalysts. The layout of catalysts and oxygen sensors is described below.
DTC Description / Detecting Condition / Confirmation Procedure
P0420, P0430
Refer to DTC P0420 / P0430: Catalyst System Efficiency Below Threshold (Bank-1 / -2). P0420 P0430
Operation:
Enable Conditions:
Typical Malfunction Thresholds:
Catalyst Monitor
Mode $06 Data:
MODE $06 Data