Catalyst Monitor

OBD SYSTEM DESCRIPTION - CATALYST MONITOR

System Description / Monitoring Procedure
Exhaust oxygen concentration at the upper part and the lower part of WU-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 controls is going on and if WU-TWC is in good condition, the output voltage of HO2S-2 is maintained at specified level. As WU-TWC becomes deteriorated, even when the above control is going on, the exhaust gas which has passed WUTWC then passes HO2S-2 at the exhaust oxygen concentration similar to that of the upper part of WU-TWC without being oxygenated or converted. Thus, waveforms of HO2S-1 and HO2S-2 output voltage become alike, ECM judges deterioration of WU-TWC by comparing waveforms of HO2S-1 and HO2S-2.

Catalyst System Layout




The system has 2 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
Refer to DTC P0420: Catalyst System Efficiency below Threshold. P0420










Catalyst Monitor




MODE $06 Data