See Figures 1 and 2
An oxygen sensor protrudes into the exhaust stream and monitors the oxygen content of the exhaust gases. The difference between the oxygen content of the exhaust gases and that of outside air generates a voltage signal to the ECM. The ECM monitors this voltage and, depending upon the value of the signal received, issues a command to adjust for a rich or a lean condition.
No attempt should ever be made to measure the voltage output of the sensor. The current drain of any conventional voltmeter would be such that it would permanently damage the sensor. Use these tools ONLY on the ECM side of the wiring harness connector AFTER disconnecting it from the sensor.
REMOVAL & INSTALLATION
For oxygen sensor removal and installation procedures, refer to Engine & Engine Overhaul of this guide. The sensor is a delicate component which must be handled properly. Be sure to follow all instructions closely when removing the sensor.