Atmospheric pollution caused by several forms of gases like methane, carbon dioxide, and nitrogen oxide was once the order of the day.
Some gases even cause ozone depletion. As a result, the authorities keep setting stricter emission regulations, and diesel vehicles’ purchase cost keeps scaling through the roof.
Automakers now design a few NOx sensors in cars that notify the driver when emissions are not as clean as they should be. That brings us to this mind-boggling question, ‘what happens when a NOx sensor fails?’
Here, we’ll discuss NOx sensor failure symptoms, causes, diagnoses, and fixes. But first, let’s look at what it is.
What Are NOx Sensors?
NOx sensors, as their name suggests, are tools for measuring and computing the concentration of nitrogen oxides in exhaust gases.
Nitrogen oxide levels in exhaust gases indicate whether there is enough oxygen available for burning. This helps ensure that the catalytic converter is working properly.
Their main job is to lessen dangerous exhaust by-products and maintain a secure atmosphere. What transpires if a NOx sensor malfunctions, you may be wondering?
The powertrain control module will turn on the dashboard’s check engine light as a result of this sensor. Additionally, you can encounter weak acceleration, low engine power output, and poor gas mileage.
NOx sensors are available in a variety of styles, and they differ from vehicle to vehicle. DFP, turbocharger, SCR catalyst, and upstream NOx sensor from the exhaust catalyst may be present in older automobiles.
Both upstream and downstream NOx sensors are standard on modern automobiles. The engine control module receives the data after they measure the exhaust emissions. How much fuel should be injected into the combustion chamber is determined by the ECM.
The exhaust pipes are equipped with the upstream and downstream NOx sensors. They operate differently and provide various advantages.
The downstream sensor computes the NOx emissions from the SCR catalyst while the upstream sensor detects the NOx emissions from the engine.
How Does A NOx Sensor Work?
As engine emission regulations become more stringent than ever, the NOx (Nitrous Oxide) sensor’s role is to analyze the emissions and determine nitrogen oxide quantities released into the environment.
The NOx sensor works by detecting the level of nitrogen oxide in the exhaust stream via an electro-catalytic mechanism, with a material that reacts with nitrogen oxides.
A voltage passed through an electrolyte can assess how much NOx is present, with the more substantial voltage representing a more significant NOx level.
Suppose the NOx sensor detects that there incorrect amount of NOx produced. In that case, it will transmit the information to the SCR system, which will then adjust the output to allow the vehicle to conform to emissions regulations.
For this reason, the NOx sensor is vital for the SCR system in cars with diesel engines to ensure that the vehicle continues to conform to the emissions standards required.
NOx Sensor Failure Symptoms
Like other car sensors, NOx sensors can fail. Whether you’re searching for NOx sensor failure symptoms on DD15 engines or BMW NOx sensor failure symptoms, here are the key signs you should watch out for.
#1. High fuel consumption.
If the NOx sensor goes bad and cannot deliver accurate information to the engine management software regarding the air-fuel mixture ratio, the car computer may not know the proper amount of air fuel to mix.
In some scenarios, this will cause the powertrain control module to compensate by mixing more fuel to ensure optimal engine performance. This is known as a rich fuel mixture.
If you have bad gas mileage on your Cummins, this could be a Cummins NOx sensor problem. It’s important to note that other factors can lead to bad gas mileage.
#2. Rough idling.
One common NOx sensor failure on Mercedes and other vehicles is rough or erratic idling. The fuel injectors inject a pre-defined amount of gas into the combustion chamber when the engine is running.
The DME oversees and electronically manages this task. But when the NOx sensor malfunctions, it causes unstable, rough, or erratic idling.
#3. Erratic acceleration.
Uneven or erratic acceleration is a common sign of a lousy NOx sensor. Here’s why; the engine control unit will compensate for the inappropriate reading by the sensor by using more fuel. In return, this will cause the vehicle to jerk when you depress the gas pedal.
#4. Engine misfire and soot buildup.
Several factors can cause an engine to misfire. However, a sudden engine misfire may mean the NOx sensor is malfunctioning. This happens when there’s little oxygen during the combustion process.
NOx sensors are one of the most costly exhaust system components because they contain platinum, which helps to reduce toxic nitrogen from the exhaust byproducts.
A lousy NOx sensor will cause higher emissions, affecting the catalytic converter. It damages the catalyst, making it unable to manage emissions. This can also lead to soot buildup. Of course, you know what this means. It’ll lead to a failed emission test.
#5. Check engine light.
While the NOx sensor is not on under the hood, it can trigger an engine check light when it goes bad. However, several reasons can cause the car computer to trigger a check engine light. Therefore, do not conclude that an engine warning light shows a lousy NOx sensor.
Diagnose the vehicle with a diagnostics scan tool to track the actual cause of the light. If you don’t have this tool, drive down to a mechanic garage for a professional inspection.
What Causes NOx Sensors To Fail?
Some factors can cause a NOx sensor to fail. Here are the probable causes of NOx sensor failures.
#1. Carbon Buildup and Contamination.
Exhaust soot, carbon deposits, and residue accumulate on the sensor element over time, degrading its ability to accurately measure NOx levels. This is especially common in vehicles with high mileage or those driven mostly in stop-and-go traffic.
#2. Oil or Coolant Contamination.
Leaks from head gaskets, valve cover gaskets, or coolant lines allow oil or antifreeze to coat the sensor, interfering with its electrochemical response. Even small amounts of contamination can cause the sensor to read incorrectly or fail completely.
#3. Thermal Stress and Age.
Continuous exposure to extreme exhaust temperatures causes the sensor’s ceramic element and internal wiring to degrade over time. Eventually, the ceramic becomes brittle, the wiring corrodes, or the sensor loses sensitivity to nitrogen oxides.
#4. Wiring or Connector Issues.
Corrosion, loose connections, or damaged wiring harnesses prevent the sensor from communicating properly with the engine control unit. Water intrusion, salt exposure, and vibration can all damage connectors and wires in the engine bay.
How to Diagnose a Faulty NOx Sensor?
- Retrieve diagnostic trouble codes using an OBD-II scan tool (available at many auto parts stores or through professional shops). Look for codes related to NOx sensor circuit, voltage, or range malfunction. Note the specific code number for reference when discussing repairs with a technician.
- Visually inspect the NOx sensor and its electrical connector for corrosion, loose connections, damaged wires, or debris while the engine is cool. Check for oil, coolant, or soot accumulation on the sensor element, which indicates contamination from internal leaks.
- Look for signs of oil or coolant leaks near the sensor and around gaskets (valve cover, head gasket, coolant hoses). Contamination from internal leaks is a common cause of NOx sensor failure and must be addressed during repair.
- If you are experienced with a multimeter and have access to your vehicle’s service manual, consult the manual for the correct sensor voltage and resistance specifications, then test the sensor’s electrical signals. If readings are out of range, the sensor likely requires replacement. Only attempt this step if you have multimeter experience and the proper service documentation; otherwise, have a professional technician perform electrical diagnosis.
- Consult your vehicle’s service manual for the exact sensor location, connector type, wiring pinout, and any special tools or procedures required for removal and inspection. Procedures, torque specifications, and connector designs vary widely by manufacturer and model year.
These diagnostic steps are general guidance only. Specific procedures, wiring diagrams, connector pinouts, sensor locations, voltage specifications, and torque values vary by manufacturer and model year.
Always consult your vehicle’s owner’s manual and service manual before performing any diagnostic testing.
If you lack experience with electrical diagnostics or do not have the proper scan tools and service documentation, have a qualified technician diagnose the issue.
How Do You Fix NOx Sensors?
You have two choices if a diagnostic reveals that your automobile has a NOx sensor issue: you may either fix the sensor or replace the defective sensor.
Since a high-quality NOx sensor is not inexpensive, you should first attempt to fix the broken one before replacing it.
- Start by removing the damaged sensor from your car using the directions in the owner’s handbook to fix it.
- You might need to do so by removing the protective rubber covering the sensor to reach it and perform the necessary repairs.
- Make careful to securely hold the sensor with electrical tape so you can see what you are working on to make the repair process easier.
- Now that you can see the sensor clearly, separate the sensor cables with a knife and some scissors.
- Once the new probe is installed, you should wrap the wires and solder them to the NOx emission control unit sensor using the appropriate color-coded cables of the new probe.
- Heat shrink tubes should be applied to the soldered regions to let the cable sheathing bond.
- After the gadget has been fixed and heated with the solder, give it some time to reach the right temperature.
If the probe was the source of the issue, the NOx sensor should now function normally and any previously present error codes should go.
If you try the aforementioned solutions and the earlier issues still exist, you should replace the sensor rather than try to fix it.
You have two choices when it comes to changing the sensor: you may buy a new sensor or a less expensive reconditioned sensor.
You should be aware that even though the refurbished NOx sensor is less expensive and occasionally might perform as well as a new one, it typically doesn’t come with a warranty.
As a result, if it malfunctions a few weeks or months after installation, you’ll need to dig deeper into your wallet to purchase a new one.
Purchasing a new NOx sensor is the best course of action. Although the sensor will be pricey, it comes with a fantastic guarantee that lasts for years.
So if the sensor breaks you can obtain a replacement at no additional cost. The breakdown must occur during the warranty term to qualify.
How much does it cost to replace a NOx sensor?
The replacement cost of a NOx sensor depends on various parameters. When budgeting how much to spend, ask yourself whether you want brand new, aftermarket, or original OEM parts.
The cost also depends on the make and model of the car. However, the average cost of NOx is between $200 to $250. Though, high-end sensors can be as high as $350 to $700.
FAQs.
Q: Can I drive with a faulty NOx sensor?
Of course, you can drive with a bad NOx sensor. However, I do not recommend it. Driving with a faulty NOx sensor for an extended period will cause several drivability issues.
It may cause poor engine power output, erratic idling, sudden engine misfire, and bad gas mileage. Before the engine starts projecting any of these problems, the ECU will trigger an engine warning light on the dashboard.
Q: How do you clean a NOx diesel sensor?
A basic NOx sensor cleaning requires soaking it in a cleaning solvent for a long period. You can soak them in a fuel injector cleaner for 3-4 hours.
After that, get a carburetor or throttle body cleaner and spray it on the NOx sensor. I recommend using carb and choke cleaner since we use it in getting rid of carbons on throttle bodies and carburetors.
Q: Can you repair a NOx sensor?
Like every component in a car, NOx sensors can fail and need fixing or replacement. Once the sensor fails, it can cause several issues, like poor engine performance, erratic acceleration, bad gas mileage, and the vehicle going into limp mode.
If you ignore these kinds of problems, things will go south quickly. Therefore, you need to repair the sensor as soon as you can. Most times, it is not the sensor that goes bad, but the lambda probes that monitor the nitrogen oxides in the exhaust gas.
Q: Do petrol cars have NOx sensors?
Automakers have seen the need to develop NOx sensors since the 1990s because of emission regulations.
The development took off in the 1990s, but in the early 2000s, manufacturers built commercial sensors on stratified charge, lean-burn gasoline vehicles with nitrogen oxides absorbers.
Manufacturers extend the development of NOx sensors to both light and heavyweight diesel engines with a urea SCR system.
Q: How long do NOx sensors last?
NOx sensor warranty on cars differs. However, on average, a NOx sensor can last between 50,000 to 60,000 miles. With proper maintenance, the sensor can last for more than that. In the same manner, it can fail long before covering 50k miles.
Final words
You’ll agree that modern-day vehicles are pretty complex and expensive. No one wants to part with his hard-earned money when problems like lousy NOx sensors spring up.
That’s why we highlighted NOx sensor failure symptoms, how to fix them, and other crucial factors concerned. Before proceeding with any repair jobs in your vehicle, ensure you’re confident enough to do it. If you are not, seek professional help.