The oxygen sensors (also known as O2 sensors) work by measuring the amount of oxygen present in your vehicle’s exhaust. Although that may not seem like an essential task, the O2 sensor is one of the most important sensors in your car. To help you understand this vital component, here’s an overview of what O2 sensors do, what causes them to fail, and some common signs your sensors needs to be replaced.

What Does the O2 Sensor Do?

The main purpose of the oxygen sensor is to ensure optimal engine performance by measuring and regulating the air-to-fuel ratio during combustion. Each combustion that takes place in the engine’s cylinders relies on the precise mix of air and fuel; when the air-fuel ratio is at the right level, your car will run smoothly. However, if there’s an excess of fuel (running “rich”) or a lack of fuel (running “lean”), you’ll experience performance issues.

The O2 sensors monitor the amount of oxygen present in the exhaust gases and relay that information to the vehicle’s onboard computer. When the mixture is too rich, the sensor sends a signal engine’s Electronic Control Unit (ECU) to decrease the fuel supply. If the mixture is too lean, the sensor sends a signal to increase the fuel supply.

Most cars have multiple oxygen sensors positioned throughout the exhaust system, with at least one located before the catalytic converter (known as the “pre-cat sensor”) and one or more positioned after the catalytic converter. The pre-cat sensor regulates fuel supply, while the downstream sensor measures the catalytic converter’s efficiency. If the O2 sensors become damaged or faulty, it can affect the exhaust system and the engine performance.

What Causes O2 Sensors to Fail?

There are three main reasons why oxygen sensors fail: age and high mileage, electrical issues, or contamination.

There are two types of oxygen sensors: unheated and heated. Unheated oxygen sensors should be inspected or replaced every 60,000 miles, as they rely on hot exhaust gas to reach operating temperature. They’re prone to contamination and need a large amount of exhaust to make contact with the active ceramic element in order to work properly—which can cause them to become contaminated over time.

Heated oxygen sensors are less prone to contamination and have an internal heat source. They should be inspected or replaced every 90,000 miles. However, since they’re made up of multiple circuits, they can be prone to electrical issues, especially if the heater circuit fails.

All oxygen sensors are exposed to harmful exhaust gases, extreme heat, and high-velocity particulates, which causes them to lose efficiency over time. Contamination can be caused by elements within the engine, such as carbon buildup from a rich fuel mixture, leaded fuel, antifreeze, or silicone residue from faulty gaskets. When this happens, it can cause the sensor to malfunction.  

Although rare, leaded gasoline can also damage oxygen sensors. Additionally, the sensors can be affected by high temperatures and general wear. This causes extended response times or a shift in the sensor’s voltage curve, and ultimately reduces the sensor’s performance.

Signs of a Faulty or Failing Oxygen Sensor

Some common signs your O2 sensor is faulty or failing include:

  • The check engine light is on
  • Decreased fuel efficiency
  • Rough idle
  • Engine misfires
  • Engine hesitation while accelerating
  • Sluggish engine performance
  • Black smoke coming from the tailpipe

While some issues are inevitable due to normal wear and tear, there are a couple of things you can do to keep your O2 sensors in good working condition. First, follow your manufacturer’s inspection and maintenance recommendations. Secondly, if you’ve noticed performance issues, don’t wait to have them addressed. The longer you wait, the more expensive they can become to repair.

If you’ve noticed any of the above signs or it’s time for scheduled maintenance, schedule an appointment with Accurate Automotive Attention! Established in 1969, we’re Yuma’s only AAA-Approved Auto Repair shop and have been voted Yuma’s Best Auto Repair 20 years in a row. With our 3-year/36,000-mile nationwide warranty on repairs and satisfaction guarantee, you can always trust that your vehicle is in excellent hands. Contact us today or request an appointment online.

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