Oxygen Sensors measure the oxygen content in the exhaust gas. Oxygen in the exhaust gas accurately indicates how complete the combustion process is. This data is transmitted to the car's ECU in real-time. The ECU then adjusts the air/fuel ratio to keep the exhaust gas in a composition that permits effective treatment by the catalytic converter.
Sensors should be tested at every tune up, and prior to smog checks. In California, 70% of the vehicle smog check failures are a result of poorly operating or failed Oxygen Sensors. In the interval periods, the following tips can show whether a sensor has reached the end of its service life:
Additionally, when the "Check Engine" light is illuminated (in vehicles so equipped), generally the Oxygen Sensor needs to be checked.
Failed and/or poorly operating oxygen sensors can cause a substantial drop in fuel economy and poor driveability. In addition, exhaust emissions can increase dramatically. Catalytic converters can also fail due to increased emissions.
While an Oxygen Sensor can completely fail, this usually happens instantaneously, and is usually due to contamination. Most sensors slowly degrade in performance and send a false rich signal to the ECU, running the engine too lean.
On-Board Diagnostic systems are in most cars and light trucks on the road today. During the 1970's and early 1980's manufacturers started using electronic controls to manage engine functions and diagnose problems. This was primarily to meet EPA emission standards. The original OBD standards in the late 1980's were derived from SAE standards for connectors and diagnostic test signals. OBD-II, a new standard introduced in the mid-'90s, provides virtually complete engine control, and also monitors parts of the chassis, body and accessory devices, as well as the diagnostic control network of the vehicle. The Environmental Protection Agency is empowered to require manufacturers to build cars that meet increasingly more stringent emissions standards. OBD-II provides a universal inspection and diagnosis method to determine that the car is performing to OEM standards.
A "universal" oxygen sensor operates the same as the OE sensor, however it does NOT come equipped with an OEM style connector. Installation requires splicing the OE connector to the oxygen sensor.
Fuel additives and injector cleaners that are labeled as "oxygen sensor safe" may be used in sensor equipped vehicles. Use of additives not labeled as "oxygen sensor safe" can damage your oxygen sensor.