Repair 7

What Are Car Oxygen Sensors

Oxygen sensors have been integrated on vehicles for more than 30 years. Located in the exhaust system, they monitor fuel-to-air ratio and catalyst efficiency. While working in a hostile environment, the sensors can eventually fail and require replacement. When this occurs, a diagnostic trouble code illuminates the check engine light to warn the driver of the component failure. Ignoring the light and not replacing the sensor can lead to further problems with the engine and emissions control system.

History

Volvo was the first auto manufacturer to feature the oxygen sensor in 1976. The sensors were specifically designed to lower emissions in the state of California to help prevent high levels of pollution. Saab soon followed suit. By 1980, almost every vehicle on the road employed one in or near the exhaust manifold. Soon, another sensor was installed into the exhaust system to monitor the efficiency of the catalytic converter. All vehicles now have at least two sensors, and some can have up to four.

Function

The upstream oxygen sensor monitors the fuel-to-air ratio for the combustible engine. A perfect mixture provides a smooth-running vehicle with lower exhaust emissions. The sensor transmits the information by radio signal to the computer of the vehicle. The computer reads the signal and makes required adjustments to the fuel-to-air mix. The downstream sensor simply monitors the catalyst efficiency and again transmits the information to the computer. When the upstream sensor fails to communicate correctly, the computer is unable to make the required adjustments and a rich or lean fuel to air mixture occurs. This causes unburned fuel to contaminate the inside of the catalytic converter.

Types

The older oxygen sensors featured a single wire to plug into the wire harness and communicate to the computer. The vehicle had to get up to operating temperature before the sensor was activated to transmit the data. This caused higher emissions to be exhausted from the engine until the sensor began to function. Newer sensors now have three to four wires. An internal heater inside the sensor heats it up more quickly to activate the function of the sensor more quickly, resulting in lower emissions.

Significance

The oxygen sensor is in place to monitor the emissions from the exhaust. Without the sensor in place or with a failed sensor, the computer cannot adjust the fuel-to-air ratio properly. This causes a rich (too much fuel) or lean (too much air) mixture. It can affect the operation of the engine and allow unburned fuel to emit down the exhaust system. When the catalyst cannot convert the unburned fuel, particles will build up on the special metals inside the catalyst. Eventually, the converter will break down inside and require replacement.

Location

As mentioned, many vehicles have multiple oxygen sensors integrated into the exhaust system. The upstream sensors are located before the catalytic converter, often near or on the manifold. Vehicles with dual manifolds will have a sensor for each. The downstream sensors are located after or in the catalytic converter. Vehicles featuring more than one converter will have one sensor for each one. Bank location of the sensors will help you determine its proper location. Bank 1 is located on the same side of the engine as the No. 1 cylinder. So a diagnostic trouble code that tells you Sensor 1 Bank 1 has failed indicates the upstream sensor on the same side as the No. 1 cylinder. Sensor 2 Bank 1 is the downstream sensor on the same side.