Oxygen Sensor: Description and Operation

Exhaust Gas Oxygen (EGO) Sensor:

Upstream oxygen sensors monitor the oxygen concentration in the engine's exhaust, and sends a signal to the Powertrain Control Module (PCM). This information is used to determine whether the mixture is too rich or too lean.

Downstream oxygen sensors are mounted in the exhaust system, behind the catalytic convertor. They monitor the efficiency of the convertor, making sure that the catalytic material has not deteriorated beyond its specification.