Oxygen Sensors - Universal

Frequently Asked Questions

What is an Oxygen Sensor?

The Oxygen Sensor is a critical component of the automotive fuel injected system, measuring and maintaining the oxygen content in the exhaust gas to ensure the optimal engine operation. To do this, an Oxygen Sensor constantly monitors the air/fuel ratio of the exhaust gas at 14.7:1, the industry’s standard for the lowest emissions. Too much oxygen in this ratio means the engine is running lean and that its performance is not optimal. Too little oxygen in this ratio means the engine is running to rich and that it’s wasting fuel and creates excess emission. Both conditions may shorten the lifespan of a vehicle’s engine and catalytic converter.

Where do I find the Oxygen Sensor?

The oxygen sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust gases exiting the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture telling the Engine Control Unit (ECU) if the mixture is burning rich (less oxygen) or lean (more oxygen) to ensure optimal engine operation.

When should I replace the Oxygen Sensor?

Due to the harsh environment of vehicle’s engine and exhaust system, an Oxygen Sensor will age gradually. “Aged” sensors will work less efficiently and respond slower than “New” sensors, therefore, this may cause premature failure of the catalytic converter. “Failing” sensors may be caused by instant or gradual contact of silicon or other contaminates. Both aged and failing sensors will cause problems such as poor fuel economy, failed emission tests, premature failure of catalytic converters, and poor engine performance.

“Aged” sensors are eminent whether through normal use or silicon and contamination. Any oxygen sensor that is defective obviously needs to be replaced. But there may also be benefits to replacing the oxygen sensor periodically for preventative maintenance. Replacing an aging oxygen sensor that has become sluggish can restore peak fuel efficiency, minimize exhaust emissions and prolong the life of the converter.

Unheated 1 or 2 wire oxygen sensors used from 1976 through early 1990s vehicles can be replaced every 50,000 to 80,000 kilometres. Heated 3 and 4-wire oxygen sensors fitted from the mid-1980s through mid-1990s applications can be changed every 90,000 kilometres. On OBD II equipped vehicles (1996 & up), a replacement interval of 100,000 kilometres can be recommended.

How do I check an Oxygen Sensor?

There are 3 methods to test an Oxygen Sensor. The most traditional method is an on car test, install the new sensor into the car and drive to see if its fuel economy and engine performance improves. The second method of sensor testing is by using an oscilloscope. An oscilloscope will check for output and response time of the sensor. The last method of sensor testing is by using a multi-meter. A multi-meter will check for function of the sensor in terms of output or no output. It will also check for ohm resistance of the sensor heater.

Common Problems

Due to the variance of application specifications; what may seem like a non-functional Oxygen Sensor may not necessarily mean a defective sensor, but an incompatible sensor. Application variations may include differences in heater resistance, and element structure. Differences in heater resistances may cause vehicle ECU to not recognize sensor output, which in turn causes the “check engine light” to turn on. The differences in element structure may mean the differences between Zirconium materials based or Titanium material based sensors. These two elements are not to be interchanged.

How do I remove the Oxygen Sensor?

The oxygen sensor should be removed from the exhaust manifold using a special oxygen sensor socket which has a cutout to clear the wires. The sensor will come out easier if the engine is slightly warm but not hot to the touch. Place the socket over the sensor and turn counter clockwise to loosen it. If it is frozen, apply penetrating oil and heat around the base of the sensor.

• Do not drop Oxygen Sensors. Dropping of a sensor may cause damage to the ceramic body of the sensor.
• Do not use an impact wrench or conventional socket type wrench to install sensor.
• Though protected by silicon sleeves, do not allow wires to touch exhaust manifold or other hot components.
• Do not expose Oxygen Sensors to water, oil, windshield cleaner, anticorrosion oil, grease, terminal cleaner, etc.
• Do not use silicon or metal additives.
• Do not use over the counter fuel additives, which are not “Oxygen Sensor Safe”
• Due to the properties of Oxygen Sensors, zirconia based sensors should not be interchanged with titania based sensors under any circumstances.

How does and Oxygen Sensor work ?

The oxygen sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.

The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style oxygen sensors breathe through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor. For this reason, grease should never be used on oxygen sensor connectors because it can block the air flow. Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.

The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading will be.

An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor output voltage will drop down to about 0.2 volts or less. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7:1, the sensor will read around 0.45 volts.

When the ECU receives a rich signal (high voltage) from the oxygen sensor, it leans the fuel mixture to reduce the sensor's feedback voltage. When the oxygen sensor reading goes lean (low voltage), the ECU reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs with different speeds depending on the fuel system. The transition rate is slowest on engines with feedback carburettors, typically once per second at 2500 rpm. Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multi-port injection are the fastest (5 to 7 times per second at 2500 rpm).

The oxygen sensor must be hot (about 300c degrees or higher) before it will start to generate a voltage signal, many oxygen sensors have a small heating element inside to help them reach operating temperature more quickly. The heating element can also prevent the sensor from cooling off too much during prolonged idle, which would cause the system to revert to open loop.

Heated oxygen sensors are used mostly in newer vehicles and typically have 3 or 4 wires. Older single wire oxygen sensors do not have heaters. When replacing an oxygen sensor, make sure it is the same type as the original (heated or unheated)

The number of oxygen sensors per engine on newer vehicles has doubled. A second oxygen sensor is now used downstream of the catalytic converter to monitor converter operating efficiency. On V6 or V8 engines with dual exhausts, this means up to four oxygen sensors (one for each cylinder bank and one after each converter) may be used.

The OBD II system is designed to monitor the emissions performance of the engine. This includes keeping an eye on anything that might cause emissions to increase. The OBD II system compares the oxygen level readings of the oxygen sensors before and after the converter to see if the converter is reducing the pollutants in the exhaust. If it sees little or no change in oxygen level readings, it means the converter is not working properly. This will cause the engine warning light to come on.