Circuit Description

The engine control module (ECM) supplies a voltage of about 0.45 V to the oxygen sensor. The oxygen sensor (O2S) varies the voltage within a range of about 1 V if the exhaust is rich, down to about 0.1 V if the exhaust is lean.

This diagnosis can detect the sluggish behavior of the lean shift of HO2S1 and detect the abnormality of HO2S2 (below 0.65 V). A malfunction is registered if the fuel trim control values exceed the maximum threshold value for the diagnosis time during fuel trim control activation phase. If catalysts are deteriorated, HO2S2 signal oscillates according to the actual lambda signal. So, the diagnosis must be considered with catalyst deterioration factor.