Oxygen (O2) Sensor

O2 sensor used in EFI system is closed-end Zirconia sensor placed in exhaust gas stream. Sensor is constructed in such way that exhaust gases pass by bottom of sensor and atmospheric air is admitted at top of sensor.

When exposed to O2, Zirconia produces electrical voltage of approximately 1.5 volts. By comparing amount of O2 present in exhaust gases to amount of O2 in atmosphere, sensor produces signal which is proportional to O2 concentration in exhaust gases.

As O2 content of exhaust gases increases relative to surrounding atmosphere, lean fuel mixture is indicated by low voltage output. As O2 content decreases, rich fuel mixture is indicated by higher voltage output. ECM interprets electrical signal and adjusts injector pulse width to maintain air/fuel ratio close to 14.7 to 1.