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Home >> Suzuki >> 2001 >> XL-7 Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 123 (Engine General Information & Diagnosis) >> H25 Engine >> Diagnostic Information & Procedures >> DTC P0420, P0430: Catalyst System (Bank-1/-2) Efficiency below Threshold >> System Description

System Description

WARNING: This page is about a different car, the 2004 Suzuki XL-7 and 2004 Suzuki Grand Vitara. However, it is still accessible from the selected car via links, so may be relevant.

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 (PCM) controls the closed loop which then controls the fuel injection volume. While the above control 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 WU-TWC 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 (PCM) judges deterioration of WU-TWC by comparing waveforms of HO2S-1 and HO2S-2.

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