Circuit Description
The heated oxygen sensor (HO2S) is used to monitor oxygen in the exhaust gas. For optimum catalyst operation, the air fuel mixture (air-fuel ratio) must be maintained near the ideal "stoichiometric" ratio. The HO2S output voltage changes suddenly in the vicinity of the stoichiometric ratio. The ECM adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric.
The HO2S generates a voltage between 0 and 1 volt in response to oxygen in the exhaust gas. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes "Lean". The ECM determines Lean when the HO2S voltage is below 0.45 volts. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes "Rich". The ECM determines Rich when the HO2S voltage is above 0.45 volts.