Circuit Description
The Heated Oxygen Sensor (HO2S) is used to monitor oxygen concentration in the exhaust gas. For optimum catalytic converter operation, the air-fuel mixture 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 0.1 and 0.9 V in response to oxygen concentration in the exhaust gas.
If the oxygen concentration in the exhaust gas increases, the air-fuel ratio is called LEAN. The HO2S voltage drops below 0.45 V, which informs the ECM of the LEAN condition.
If oxygen is not in the exhaust gas, the air-fuel ratio is called RICH. The HO2S voltage increases above 0.45 V, which informs the ECM of the RICH condition.
HINT:
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The HO2S heater circuit uses a relay on the +B side of the circuit.