Oxygen sensor (O2 sensor) is used for Air-Fuel Ratio (AFR) or Lambda monitoring and control for ECU tuning of vehicle fuel economy and speed control. Here we discuss the testing methods for zirconia and titanium oxygen sensors, oxygen sensor failure mechanisms, the causes of oxygen sensor failures, and when-how to replace the bad/failed oxygen sensors. When the engine is first started, the in-vehicle computer is in “open loop” and does not use the signal from the O2 sensor. The fuel mixture is set to run rich and stays that way until the system goes into “closed loop” and starts using the O2 sensor signal to vary the fuel mixture. A dead sensor will prevent the onboard computer from making the necessary air/fuel corrections, causing the air/fuel mixture to run rich in the “open loop” mode of operation, resulting in much higher fuel consumption and emissions. oxygen sensor failure may be damage to your vehicle’s catalytic converter – a very expensive way to find out your oxygen sensor needs replacement!

Testing of Oxygen Sensors (O2 sensors)

The O2 sensor can be checked by removing it from the vehicle, connecting a digital voltmeter to the sensor and using a propane torch to heat the sensor element. Some vehicles (Jeep & Toyota) have “titania” O2 sensors that change resistance rather than produce a voltage. This type of O2 sensor can be tested with an ohmmeter and propane torch. While testing the oxygen sensors, you must be careful to not *apply* voltage to the sensor, but measuring it’s output voltage is not harmful.

Symptoms of Oxygen Sensor (O2 sensor) Failures

  • Sensor Light on dash indicates problem. Lambda sensor failure may be indicated possibly by the illumination of a ‘check engine’ light.
  • Increased tailpipe emissions
  • Increased fuel consumption thus reduced fuel economy
  • Hesitation on acceleration
  • Stalling and Rough idling of vehicles

Causes for Oxygen Sensor (O2 sensor) Failures

Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles (50,000 to 80,000 km). Heated sensor lifetime is typically 100,000 miles (160,000 km). The normal aging process will eventually cause the oxygen sensor to fail. However, the sensor may also fail prematurely if it becomes contaminated with lead from leaded gasoline, phosphorus from excessive oil consumption or silicone from internal coolant leaks or using silicone sprays or gasket sealers on the engine. Environmental factors such as road splash, salt, oil and dirt can also cause a sensor to fail, as can mechanical stress or mishandling. Applying an external voltage to the zirconia sensors, e.g. by checking them with some types of ohmmeter, may damage them.

When to Replace damaged Oxygen Sensors (O2 sensors)

Air-fuel ratio (AFR) sensors should be replaced according to the vehicle manufacturer’s guidelines. In general, oxygen sensors should be checked every 25,000 to 30,000 miles and renewed every 60,000 to 80,000 miles.

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