NOx sensors are mounted on the exhaust system before the catalytic converter. They measure the levels of nitrogen oxide for the engine’s computer, adjusting the valve timing and fuel mixture.

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Now that is out of the way, let’s proceed.

Like other parts of your car, NOx sensors fail, and they do it for many reasons. Here are 7 NOx sensor failure causes and how you can prevent them from happening:

Water

Water can come from the inside or outside of the exhaust. If you live in areas that rain a lot or regularly drive in water, it’s not unusual for the plugs connecting the NOx sensor to corrode and prevent the sensor from functioning correctly. As you can guess, all you need to do to get rid of this problem is to replace the plugs.

Sometimes you will have water inside the exhaust because of condensed air moisture or as a side product of the work of CO catalytic converters.

To prevent this damage, avoid driving in deep waters. To discharge water that might have condensed in the exhaust, make it a habit to drive more regularly and over longer distances.

Mechanical damage

The most common culprits for mechanical damage are stones as you are driving. While the NOx sensor is pricy, the vital measuring element is thin and fragile, so even a minor impact can significantly damage it. This means that when your exhaust is hit with substantial force, the sensor is likely to die.

It’s often hard to avoid this kind of damage, but you can minimize it by driving carefully on gravel or large (higher) barriers.

Leaky Injectors

The unburned fuel gets into the exhaust when your injectors are leaking and ignite. In the event any of the cylinders are misfiring, oxygen gets in the exhaust.

Fuel and oxygen are the perfect combination for burning and even exploding, putting your NOx sensor and even the entire engine in danger.

The cool thing is that when you are having leaky injectors, the engine gives plenty of signs such as shivering, lighting up the engine light, and permanent vibration when cold starting.

When you experience any of these symptoms, you have a leaky injector. You should address the leak as soon as possible to avoid damaging the NOx sensor, lambda probes, and sometimes CO catalytic converters.

Rapid Temperature Changes

Near the NOx sensor, the exhaust is hundreds of degrees hot, so when water splashes on the area, there is the risk of the sensor suffering from thermal shock and getting damaged.

The sensor is likely to suffer from thermal shock when you drive into a deeper puddle or snowdrift. When water or snow reaches the exhaust, the temperatures drop sharply, leading to the damage of the NOx sensor.

Like mechanical damage, it’s hard to avoid this kind of damage, but you can be more cautious when driving in wet or snowy conditions. Always avoid driving at high speeds to avoid getting into a deep puddle or snow drifting.

Engine Additives

There are all manner of engine additives. There are oil additives to improve the performance of the engine, additives to clean the valves and cylinders, additives to improve compression, increase power, reduce the exhaust gasses, and so on.

In most cases, these additives damage the CO catalytic converters, cause Lambda problems, and lead to injector leaks that burn and damage the NOx sensors.

To avoid the faults resulting from the additives, avoid using them at all costs.

Enriched Fuel

When you top up your car with enriched fuel, the fuel gets in the exhaust, where it burns and forms soot. The soot then sticks to the NOx sensor probe, and as a result, it can’t feel the contents of the exhaust gasses.

To avoid this, avoid taking enriched fuels. This calls for you to be cautious of where you fuel your car. As a rule of thumb, only fuel at reputable gas stations.

To confirm that your sensor is functioning optimally, regularly take your car to a specialist for inspection.

Too Much Oil In The Engine

When there is too much oil in your engine, plenty of it gets burned and settles in the exhaust. It also goes to the Lambda probes and CO catalytic converters and damages them.

To avoid damaging your sensor with oil, avoid adding too much than necessary to your engine. If you have noticed that, your engine is consuming more oil than normal, get to the bottom of it and find out why that is happening.

What Happens When The NOx Sensor Fails?

Plenty of things happen. 

Right off the bat, you have general SCR system faults, since the NOx sensors are directly linked to the SCR system. You also have multiple faults on your dashboard that cap your vehicle’s power, and it functions in Limp mode.

What To Do About The Failed Sensor

When your sensor fails, replace it. Replacing the sensors is pricy, so you should have a large budget.

New sensors are always the best as they have warranties, but if you don’t have money for them, there are plenty of refurbished units you can go for. You can find these in service shops, garages, and part stores.

The refurbished parts are 1.5 times cheaper than new parts and will serve you as well as new parts. Their only downfall is they don’t have a warranty, so when they fail, you install new ones from your pocket.

If you don’t want to install another NOx sensor, you can use a NOx emulator. The emulator imitates the workings of a NOx sensor and lets the engine know what is going on. The beauty of emulators is they are easy to use and several times cheaper than NOx sensors.

You can also use them with a faulty catalyst and this saves you even more money you would have spent on repairs.

When buying the emulators, buy from a reputable brand. They also should come with at least a 2-year warranty and 30 days refund guarantee.