Oxygen (O2) Sensor

The O2 sensor used in EFI system is placed in exhaust gas stream. Sensor is constructed in such way that exhaust gases pass by bottom of sensor. When exposed to O2, sensor produces electrical voltage. This voltage ranges from approximately .1 volts (high O2-lean mixture) to .9 volts (low O2-rich mixture). 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 14.7:1.

NOTE: No attempt should be made to measure O2 sensor voltage output. Current drain of conventional voltmeter could permanently damage sensor, shift sensor calibration and/or render sensor unusable. DO NOT connect jumper wire, test leads or other electrical connectors to sensor.