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 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.

Catalyst A/F Sensor And HO2S Layout:

Catalyst, A/F sensor and HO2S layout

DTC Description / Detecting Condition / Confirmation Procedure

P0420, P0430
Refer to DTC P0420 / P0430:Catalyst System Efficiency Below Threshold (Bank -1/-2). P0420

Catalyst Monitor:

Enable Conditions:

Typical Malfunction Thesholds:

Catalyst Monitor

MODE $06 Data:

MODE $06 Data