Exhaust Gas Oxygen (O2) Sensor

The O2 sensor, mounted in the exhaust system, monitors quantity of oxygen in exhaust gas. O2 sensor is constructed of metals (platinum and rhodium), which produce a small voltage when hot and in the presence of oxygen. O2 sensor output voltage is checked with a DVOM with 10-megohm impedance.

A lean combustion condition, which has a large oxygen content, produces a low voltage signal (approximately .1 volt). A rich combustion condition, which has a low oxygen content, produces a higher voltage signal (up to .9 volt). The ECM uses O2 sensor signals to compute fuel injector pulse signals.