Oxygen Sensor

This sensor is mounted in engine exhaust stream, in front of catalytic converter. It supplies a low voltage (under 1/2 volt) when fuel mixture is lean (too much oxygen) and a higher voltage (up to 1 volt) when fuel mixture is rich (not enough oxygen).

Oxygen sensor must be hot (over 480°F/250°C) to function properly and to allow ECU to accept its electrical signals. The oxygen sensor measures quantity of oxygen only.

California vehicles are equipped with a special electrically heated oxygen sensor. This oxygen sensor reaches operating temperature sooner and also begins to function earlier. The heated oxygen sensor has 3 wires, 2 for the heater element (power & ground), and a single wire for the oxygen sensor signal.

The heating begins with ignition on (via fuel pump & DME relay terminal 87). The plugs from the sensor to the wiring harness are located near the flywheel sensor plugs (speed, reference mark).

NOTE: No attempt should be made to measure oxygen sensor voltage output. Current drain of conventional voltmeter could permanently damage sensor, shift sensor calibration range and/or render sensor unusable. Do not connect jumper wire, test leads or other electrical connectors to sensor. Use these devices only on ECU side of harness after disconnecting sensor.