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How to Spot the Signs of Trouble
with Your NOX Sensors

You’re cruising along down the road when suddenly, a light flashes on your engine’s dashboard. Your heart immediately starts to race because a warning light on your dashboard is never a good thing. The indicator tells you that something is not right with the NOx sensor in your vehicle. 

If this is something that has happened to you recently and you’re wondering how to better prepare for another NOx problem in the future, then you need to read this guide.

NOx Sensors Explained

A NOx sensor is a little device that helps you monitor the amount of nitrogen oxide that is emitted by your vehicle. The NOx reduction after-treatment system, which typically includes a turbocharger, a DPF, and an SCR catalyst, to mention a few components, includes the sensor. The NOx sensor is placed directly upstream of the catalyst, where it can provide the most precise urea injection measurement.

In your vehicle, your NOx sensor has a job to do. It’s job is to keep an eye on the NOx gas content in exhaust fumes that travel through the system. On their way out, these exhaust fumes are measured by the sensor. Essentially, your NOx sensor is effectively serving as the catalyst's supervisor, monitoring its performance and ensuring that everything is functioning well. Without a NOx sensor, the new Euro 6 standards would be impossible to meet. Your NOx sensors keep the manufacturers working hard trying to keep diesel engines alive as per the laws and regulations that have tightened on internal-combustion engines. Manufacturers are now having to work harder than ever before in order to make them more efficient, and this is why they rely heavily on the NOx sensors. 

How Your NOx Sensor Works Hard

If your car was a person, the ECU would be its brain. The NOx sensor transmits important, real-time information about the amounts of NOx and O2 in the system to the ECU. These measurements may then be used by the ECU to alter valve timing and fuel mixture in real time, improving engine efficiency, boosting fuel economy, and lowering hazardous exhaust emissions.

Is There a Warning Leading Up to the Failure?

Unfortunately, the NOx sensor normally fails without warning. You usually won’t know something is wrong until that warning light starts to light up on your dashboard. Luckily, however, it is a simple problem to detect. What is even luckier is that it is a problem that is much easier to correct. All you need to do is get a replacement sensor. There may not be a lot of warning signs beforehand, but if you keep an eye out, you could spot these few indicators that a new sensor is required:

  • Your Engine Warning Lights Come On - This will be perhaps the most apparent sign that you could have some trouble with your NOx sensors. However, it is also certainly the one that most people overlook. Despite the fact that the NOx sensor is not positioned within the engine bay, if it fails, an engine warning light will still illuminate. While this is not a foolproof technique for detecting NOx sensor problems, it does provide you a much clearer picture of what's going on with your automobile. After a check engine light comes on, scanning for error codes generally indicates if you're dealing with a faulty NOx sensor immediately away. 
  • Your Idle Is Unstable - A malfunctioning NOx sensor is the most common cause of irregular idling. For even idling, fuel injectors must maintain a particular fuel flow into the combustion chamber, a duty that the DME regulates electronically. Since your engine’s ECU has no means of understanding what's going on with the engine, your ECU will then be forced to assume the worst. This is a precautionary measure on its part. Gasoline injectors that are meant to provide a continuous supply of fuel to the engine can starve and or surge on occasion. When the NOx sensor fails, the fuel starves and surges, resulting in uneven idling. If you've observed that the automobile won't stay at a certain rpm, a defective NOx sensor might be the cause. In either scenario, this is bad for your automobile in the long term. 
  • Your Fuel Consumption Shoots Up - Have you noticed that your fuel consumption has been on the higher side lately? If this is not normal for your vehicle, it could be an indication that something is up. This might happen if your NOx sensor is not operating properly. This will then trigger the ECU because the ECU will not receive any information about the state of the exhaust gases. When this happens, the computer will not be able to calculate the required fuel mixture or air-to-fuel ratio, hence triggering the NOx failure. This will then compel the ECU to consider the worst-case situation and run a rich fuel mixture in difficult circumstances to assure maximum power.

What You Should Do Next

The problems above are merely indicative that there could be a problem with your NOx sensor. To accurately determine the problem, an assessment by your auto technician is still required. Your auto technician will be the best person to advise you on what your next steps should be after the initial assessment. Because a good quality sensor is not exactly on the cheaper side of things, you should try to repair the damaged sensor first. If all else fails, only then should you consider replacing your NOx sensor. 

Looking after your vehicle is one of the easiest ways to minimize problems with your NOx sensor. All it takes is some regular looking after and better driving tips while you’re on the road to help increase the lifespan of your sensors. For example, when driving on gravel, you should also use extreme caution and don't drive rapidly on uneven surfaces. This will help to limit the risks of pebbles, twigs, and other debris striking the exhaust and damaging the installed NOx sensor. Longer car rides are preferable too, since they burn all the water in the exhaust and thus ensure that it doesn’t do any damage to your sensor. 


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