What's An Oxygen Sensor, and Why Is It Important?

The oxygen sensor is a tube-shaped device that monitors the oxygen level in the engine's exhaust. It is typically mounted inside the exhaust manifold.

Also called lambda sensors or O2 sensors, oxygen sensors play a big part in controlling your vehicle’s emissions. When they are working correctly, you will have a good running vehicle with good fuel economy. If they fail, your vehicle will be less fuel efficient and probably won't pass emissions testing.

Depending on which Nissan you own, you could have one to four oxygen sensors inside your exhaust system. Older vehicles may only have one sensor. Newer vehicles with a V6 or V8 engine typically have four oxygen sensors.

How an Oxygen Sensor Works

Nissan o2 sensor

The oxygen sensor measures the amount of oxygen in the exhaust. It also compares the amount of oxygen in the exhaust to the amount of oxygen in the air immediately surrounding your vehicle.

As soon as the sensor gets a reading, it communicates the data to the ECU. This happens up to 7 times per second. The ECU uses the information to adjust the fuel/air mixture. It does this by increasing or decreasing the amount of fuel injected into the chambers. The ECU is attempting to provide the optimum fuel mixture at all times.

  1. Optimum Fuel Mixture - Provides best fuel economy, best power, and least emissions.
  2. Rich Fuel Mixture (too much fuel vs air) - Reduces fuel economy and power, and increases emissions. "Running rich" too long can cause buildups in the catalytic converter(s) that will cause premature failure. A dirty air filter can cause an engine to run rich.
  3. Lean Fuel Mixture (too much air vs fuel) - The ECU retards timing to prevent detonation, which reduces fuel economy and power. "Running lean" too long can shorten spark plug life.

The 5 Most Common Tell-Tale Signs of a Failing Oxygen Sensor

Modern oxygen sensors will last up to 100K miles, but they will always eventually wear out. Since they’re exposed to extreme heat and byproducts of combustion (such as lead, fuel additives, ash, etc.), it’s common for them to fail sooner than that. In fact, oxygen sensor failure is quite common. Keep an eye (and ear) out for the following symptoms:

  1. Poor idle.
  2. Decreased fuel economy.
  3. Check engine light is on.
  4. Failed emissions testing.
  5. Trouble starting the engine.

Diagnosing and Repairing a Failing Oxygen Sensor

You can bring your vehicle to the nearest Nissan dealership and have them do a diagnostic check. The most common codes for oxygen sensor failure are P0138 and P0135.

Oxygen sensor dtc code

Image Credit: Truck Master

You could also choose to diagnose the problem yourself. You can save a hundred bucks or so by replacing the bad one yourself. An authorized online seller like Nissan Parts Plus is a great place to purchase an OEM replacement oxygen sensor. Oxygen sensors are usually easy to access and replace. You just need ramps or jack-stands, some mechanical experience, and a wrench. Here’s a handy tutorial on replacing an oxygen sensor yourself.