Like any other car part, the NOx sensors also fail, and you have to fix or replace them to restore your car to proper working condition. Luckily, when the sensors fail, they give several symptoms that include:

The engine warning lights come on.

While the NOx sensor isn’t mounted on the engine bay, its failure can result in the engine light coming on. But, of course, the engine warning light can come on due to plenty of reasons, so don’t rush to conclude that it’s coming on due to the NOx sensor problems.

If you have an error code analyzer, you should use it to analyze the errors but if you don’t have the analyzer, take your car to an experienced professional to help you with the diagnosis and analysis.

Your car can have plenty of error codes, and different codes have different meanings. For example, if you have a BMW car, some of the error codes that you might have include:

• 2AF2: 2B06; 2B09 nitric oxide sensor, Lambda linear
• 2AF4: 2B07; 2B0A NOx sensor, electrical
• 2AF6: 2AFB; 2B0B nitric oxide sensor, Lambda binary
• 2AF9:  NOx sensor, NOx signal: coast mode check
• 2EAE:  NOx sensor message missing (timeout)
• 30D6:  nitric oxide sensor, plausibility
• 30D8:  NOx sensor, Sensor damaged
• 30DA:  NOx sensor, heating time
• 30DC: nitric oxide senor, heating
• And many others

Increased fuel consumption

Have you noticed that your car has suddenly started consuming a lot of fuel? It could be due to a faulty NOx sensor. 

Without the sensor sending information to the engine, the engine management system can’t tell how the engine works in terms of fuel mixture and air-to-fuel ratio.

And due to this, the engine’s electronic brain assumes that your car is in the worst condition and enriches the fuel mixture to provide maximum power to the car.

It’s hard to be sure that the problem is due to a faulty NOx sensor, so before you jump to a conclusion, take your car to an experienced professional and have it inspected.

Erratic idling

In most cases, erratic idling is due to a faulty NOx sensor. 

Fuel injectors have to maintain a certain fuel flow into the combustion chamber for even idling, a task that the DME electronically manages.

When the NOx sensor is faulty, the starving and surging of the fuel results in uneven idling, therefore, if you have noticed that the car isn’t sticking to a given rpm, a faulty NOx sensor might be the reason.

Again, since you aren’t a mechanic, don’t conclude that the uneven idling is due to the sensor problem. Instead, take your car to a professional mechanic and have the problem professionally diagnosed.

How do you fix a faulty NOx sensor?

If you have run a diagnostic and determined that your car has a NOx sensor problem, you have two options: repairing the sensor or replacing the faulty sensor.

A good quality sensor doesn’t come cheap, so you should try to fix the faulty sensor and only replace it if you have failed to repair it.

• To repair the sensor, begin with taking the faulty sensor from your vehicle, following the instructions given in the vehicle’s manual. 
• To do it, you may need to pull back the protective rubber covering the sensor to gain access to the sensor and do the repair work.
• To have an easy time doing the repair work, ensure that you tightly grip the sensor with electrical tape to see what you are working on.
• Now with a clear view of the sensor, split the sensor cables using a knife and a pair of scissors.
• You should then connect the corresponding color-coded cables of your new probe to those protruding from the NOx emission control unit sensor, and once the new probe is in place, wrap the wires and solder them in place.
• To allow the cable sheathing to bind, use heat shrink tubes on the soldered areas.
• After soldering and applying heat to the newly repaired device, leave it for a few minutes to attain the correct temperature.

If the problem was with the probe, the NOx sensor should now run properly, and the error codes that were there before should go away.

If you do all of the above and the previous problems persist, you should replace the sensor instead of repairing it.

When it comes to replacing the sensor, you have two options: Replacing it with a new sensor, such as https://www.dpfpartsdirect.com/products/2872942-surplus-sensor-temp-title or getting a cheaper refurbished sensor.

You should note that while the refurbished sensor is cheaper and might sometimes work as well as a new one, in most cases, it doesn’t come with a warranty, so when it breaks down after a few weeks or months of installation, you have to go back to your pocket and buy a new one.

The safest way out is to get a new NOx sensor. While the sensor will be expensive, it comes with a great warranty covering you for years, so when the sensor fails, you get a replacement at no extra cost on you. The only qualification has to be that the failure happens within the warranty period.

Can you prevent the NOx sensor from failing?

Yes, you can do it by taking good care of your car. 

One of the things you should do is to minimize water condensation in the exhaust by avoiding short trips. If possible, stick to longer car trips as they burn all the water in the exhaust so that none finds its way into the sensor and destroys it.

You also should take ultra care when driving on gravel. As a rule of thumb, don’t drive fast on rough surfaces to reduce the chances of rocks, sticks, and other materials hitting the exhaust and damaging the mounted NOx sensor.

Finally, you need to be cautious of the type of fuel you put in your car. To prevent your sensor from being damaged by excessive soot from the exhaust, only put high-quality fuel in your car. This calls for you to avoid fueling in no-name gas stations.