Bad Oxygen Sensor Symptoms and Causes

With all the unique sensors your vehicle utilizes daily, perhaps one of the more vital sensors is the O2 sensor, which is needed for a car to drive at its top-notch capability. With all of the exhaust gases a car creates, it’s important to have something that knows the O2 levels in the exhaust gases.

The sensor has an important part to play in keeping track of a vehicle’s O2 amount to make sure the engine is efficiently burning its fuel. A functional oxygen sensor can be an essential cog for a consistent running car.

Still, a poor oxygen sensor can most likely cause poor fuel economy, bad smells in your vehicle, and a poorly performing powertrain. Here you’ll learn more about things to look out for when using your vehicle that can be easy-to-see signs of a failed oxygen sensor.

What Does an Oxygen Sensor Do?

O2 sensors measure oxygen levels in your exhaust fumes to gauge engine ‘efficiency’.

Gas engines work by combusting an air-fuel mixture in the engine cylinders. This mixture needs to be burned at a precise ratio to perform as efficiently as possible.

If this ratio is off, the mixture in the engine is considered “rich” if there is not enough oxygen in the mixture, or “lean” if there is too much oxygen — both of which can cause harmful emissions and potentially damage your engine.

The oxygen sensor detects rich or lean mixtures and tells your Powertrain Control Module (PCM) to adjust the ratio. The PCM will then inject more or less fuel into the engine.

Many standard vehicles come with at least two oxygen sensors. The second sensor also measures oxygen in the exhaust flow, but only after the exhaust fumes have passed through the catalytic converter.

Catalytic converters convert certain unwanted exhaust gases to help control the release of toxic emissions. This second O2 sensor is placed downstream of the catalytic converter to measure how efficiently it converts the exhaust.

Signs of a Bad Oxygen Sensor

When your oxygen sensor goes bad, it’s only a matter of time before you start experiencing some of the symptoms below:

#1. Poor Fuel Efficiency.

If you find yourself filling up the gas tank more often than usual, a faulty oxygen sensor might be to blame. It can lead to an incorrect air-fuel mixture, causing your car to burn more fuel.

#2. Check Engine Light.

The illuminated check engine light on your dashboard could indicate various issues, including a malfunctioning oxygen sensor. Don’t ignore this warning; have your vehicle’s diagnostics checked.

#3. Rough Idling or Stalling.

A bad oxygen sensor can cause your engine to idle roughly or even stall when you’re at a stop. This is due to the improper air-fuel mixture affecting engine performance.

#4. Difficulty Accelerating.

If your car struggles to accelerate smoothly, it might be due to a malfunctioning oxygen sensor disrupting the engine’s performance.

#5. Increased Emissions.

Failed oxygen sensors can lead to higher emissions. If your vehicle fails an emissions test or you notice excessive tailpipe smoke, it could be a sign of a problem.

#6. Unusual Exhaust Odor.

A malfunctioning oxygen sensor can result in an irregular air-fuel mixture, leading to an odd odor coming from your exhaust.

#7. Sudden Drop in Gas Mileage.

If your car’s fuel efficiency takes a sudden dip, you must inspect the health of your oxygen sensors or seek some mechanic assistance as they play a key role in optimizing fuel usage.

#8. Sensor Codes in Diagnostics.

Modern vehicles have onboard diagnostics systems that can pinpoint specific issues. If you receive an error code related to the oxygen sensor (such as P0130 or P0135), it’s a clear sign that there’s a problem.

Can You Drive with a Bad Oxygen Sensor?

The short answer is “Yes,” your vehicle’s engine can operate without oxygen sensors. But without them, your PCM won’t know how much fuel to inject into the engine.

Depending on how it fails, you may end up with an overly rich fuel mixture, drastically reducing fuel economy and clogging your catalytic converter with excess, unburnt fuel.

This excess may become burnt in the catalytic converter, raising its temperature and potentially shortening its lifespan. 

Note: It’s much cheaper to replace an oxygen sensor than a catalytic converter. 

So are oxygen sensors necessary? Yes. While the damage may seem small initially, the longer you drive with a bad oxygen sensor, the worse the damage will become.

Eventually, you may experience rough idling, poor acceleration, engine misfires, an illuminated check engine light, and failed emission tests.