Mercedes Benz NOx Sensor Issues and how to fix it?
A failing NOx sensor on a Mercedes-Benz diesel shows up as a check engine light, higher fuel use, rough idle, jerky acceleration and, in the end, a failed emissions test. The usual causes are soot build-up on the probe and burnt or damaged wiring. The fix is to read the fault codes with a scan tool, inspect the sensor and its harness, clean or repair the probe if that is the problem, and replace the sensor if it still reads wrong.
TL;DR
- Symptoms: check engine light, poor fuel economy, erratic idle, uneven acceleration, misfires and soot.
- Causes: soot (smog) on the probe, burnt or damaged wiring harness, broken internal connections.
- First step: scan the car with an OBD2 tool to confirm the NOx sensor is really at fault.
- Fix: clean the sensor (soak 3 to 4 hours in injector cleaner), repair the probe wiring, or replace it.
- Cost: around $250 to $300 for a typical Mercedes NOx sensor, $400 to $800 for high-end ones.
- Life: roughly 50,000 to 60,000 miles on average; Bosch rates its sensor at 15,000 hours.
- If this is not your case, read the Sprinter AdBlue heater failure guide.
Table of Contents
- What Is a NOx Sensor?
- How Do NOx Sensors Operate In Mercedes Benz?
- What Issues are You Likely to Encounter In a Mercedes Benz with NOx Sensor Failure?
- What Leads to NOx Sensor Failure In Mercedes Benz?
- How are NOx Sensors Fixed In Mercedes Benz?
- Can I Drive My Mercedes Benz If the NOx Sensor Is Broken?
- How Is a NOx Diesel Sensor Cleaned for Mercedes Benz?
- How Much Does a Mercedes Benz NOx Sensor Replacement Cost?
- Can a Mercedes Benz NOx Sensor Be Repaired?
- Do Petrol Driven Mercedes Vehicles Have NOx Sensors?
- What Is the Lifespan of Mercedes NOx Sensors?
- The Conclusion
What Is a NOx Sensor?
NOx sensors, as their name suggests, are tools for counting and recording the number of nitrogen oxides in exhaust gases. Nitrogen oxide levels in exhaust gases indicate if there is enough oxygen available for burning. This makes it easier for the catalytic converter to work effectively.
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Their main job is to lessen dangerous exhaust byproducts 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 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 Do NOx Sensors Operate In Mercedes Benz?
Image source -https://www.bosch-mobility-solutions.com/en/solutions/exhaust-gas-treatment/nox-sensor/
A NOx sensor is a part of an SCR system that calculates how much NOx is present in an exhaust system. This enables the SCR to determine the ideal urea or ammonia concentration for higher fuel efficiency and less hazardous emissions into the atmosphere.
Some NOx sensors track the bulk of exhaust flow in addition to counting the nitrogen oxides in the exhaust stream.
Modern automobiles include advanced NOx sensors that contain certain substances that respond to nitrogen oxides. Catalysts are these substances, which are often produced using titanium oxide, activated carbon, and other base metals.
These substances transmit a voltage that is linked to the concentration of nitrogen oxide. The voltage increases as the amount of nitrogen in the exhaust stream increases.
Less sophisticated NOx sensors monitor the exhaust gas, remove the oxygen, and measure the NOx content.
Bosch, which supplies NOx sensors for SCR systems, publishes these figures for its current NOx sensor:
| Bosch NOx sensor spec | Value |
|---|---|
| Measuring range | 0 to 3,000 ppm |
| NOx accuracy at 0 ppm | ±5 ppm |
| Max. temperature of the sensor control unit | 140 °C |
| NOx response time | about 1,000 ms |
| Design lifetime | 15,000 hours |
The sensor is a probe plus a sensor control unit joined by a wiring harness, which is why damaged wiring is such a common fault.
What Issues are You Likely to Encounter In a Mercedes Benz with NOx Sensor Failure?
NOx sensors can malfunction just like other auto sensors. These are the warning signs to look out for, and they are much the same on Mercedes, DD15 or BMW diesels.
| Symptom | Likely cause | Fix |
|---|---|---|
| Check engine light | Sensor reading out of range, or another fault | Scan the codes before blaming the sensor |
| Excessive fuel use | Wrong reading makes the ECU run a rich mixture | Clean or replace the sensor |
| Erratic idle | Faulty sensor signal upsets injection | Check wiring, then the sensor |
| Unsteady acceleration | ECU adds extra fuel to compensate | Clean or replace the sensor |
| Misfire and soot build-up | Not enough oxygen during burning | Fix the sensor before the catalyst is damaged |
| Failed emissions test | Damaged catalyst from high emissions | Replace sensor, check the catalytic converter |
If the exhaust is also loaded with soot, read the Sprinter DPF clogged guide.
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1. Excessive Fuel Use
The auto computer could not know the correct quantity of air-fuel to mix if the NOx sensor malfunctions and is unable to provide accurate information to the engine management software on the air-fuel mixture ratio.
In some circumstances, the powertrain control module will respond by compensating by blending extra gasoline to guarantee optimum engine performance. This fuel combination is referred to be rich.
It may be a Cummins NOx sensor issue if your Cummins is getting poor gas mileage. It's significant to remember that poor gas mileage might result from other issues.
2. Erratic Idling
Rough or unpredictable idling is a typical symptom of NOx sensor failure in Mercedes and other automobiles. When the engine is operating, the fuel injectors send a precise amount of gas into the combustion chamber. The DME is in charge of managing this electronically. However, a faulty NOx sensor might result in inconsistent, harsh, or unstable idling.
3. Unsteady Acceleration
Acceleration that is uneven or irregular is a frequent indicator of a bad NOx sensor. Here's why: the engine control unit will use extra gasoline to make up for the sensor's inaccurate reading. As a result, the car will jolt when you hit the throttle pedal.
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4. Misfiring Engines and Soot Accumulation
An engine's misfiring can be caused by many things. However, a sudden engine misfire might indicate a broken NOx sensor. When there is insufficient oxygen present during burning, this occurs.
Due to the platinum they contain, which aids in reducing harmful nitrogen from exhaust emissions, NOx sensors are one of the most expensive parts of the exhaust system.
Higher emissions from a bad NOx sensor will have an impact on the catalytic converter. The catalyst is damaged, rendering it incapable of controlling emissions. Soot accumulation may also result from this. You are aware of what this entails, of course. It will result in the emission test failing.
5. The Check Engine Light Comes On
Under the hood, the NOx sensor is off, but when it malfunctions, it might turn on the engine check light. The check engine light, however, might be activated by the automobile computer for many reasons. So, don't assume that a malfunctioning NOx sensor is the cause of an engine warning light.
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To determine the true reason for the light, scan the car using a diagnostics tool. Drive down to a mechanic's shop for a professional examination if you don't have this tool. What might cause a NOx sensor to malfunction after seeing the symptoms?
What Leads to NOx Sensor Failure In Mercedes Benz?
A NOx sensor may malfunction for a variety of reasons. These are the most likely reasons why NOx sensors fail.
Smog: Given where these sensors are located, it is not surprising that smog can harm them. Although soot accumulation is a symptom of a bad NOx sensor, it is also a typical cause.
Burnt or damaged cables: The NOx sensor's failure may be due to a burnt or damaged wiring harness. A virtual examination in this situation will identify the offender.
The NOx sensor may not necessarily be defective. The internal connections that read the NOx level can be broken.
These are the typical causes, though there may be more. Often a visual examination is all you need to find the source of the NOx sensor failure.
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How are NOx Sensors Fixed In Mercedes Benz?
Use a diagnostics scan tool to identify the car if you detect two or more of the problematic NOx symptoms listed above. This will enable you to establish whether the sensor is malfunctioning or whether the symptoms point to another system issue.
You can have a defective probe or a damaged or broken sensor. First, locate the sensor on the exhaust pipe and carry out a visual examination. If the probe is the problem, take these actions to resolve it.
1. Remove the NOx Sensor
The NOx sensor should now be free of the exhaust pipes. For a detailed illustration of the sensor position for your model, consult your owner's manual. The removal of the NOx sensor is also covered in the guide.
What Tools Do You Need?
To complete this repair, you'll need a few standard tools. You'll need the following equipment.
- The Scissors
- A Knife/cutter
- An Electronic tape
- Iron for soldering
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2. Reposition the Dust Cover
To reach the NOx sensor, pull aside the dust cover. Use electrical tape to secure the dust cover so it won't move while the sensor is being repaired.
3. Divide the Probes
Use a cutter or knife to cut the probes in half. Avoid cutting all the cables at once. Be certain that they are not the same length.
4. Install the New Probes and Cables
Obtain the replacement probes, then properly connect them. According to color, connect the probes. And now carefully wrap and solder the wires.
5. Examine the NOx Sensor Once More
Once the probe problems have been resolved, rediagnose the car to make sure everything is operating as it should. Replace the NOx sensor if the diagnosis reveals any problems, or get in touch with your mechanic.
Can I Drive My Mercedes Benz If the NOx Sensor Is Broken?
Yes, it is possible to drive your Mercedes-Benz with a damaged NOx sensor. I do not, however, advise it. Long-term driving with a damaged NOx sensor will result in several drivability problems.
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Poor engine power output, unpredictable idling, unexpected engine misfire, and poor gas mileage are all possible effects. The ECU will activate an engine warning light on the dashboard before the engine exhibits any of these issues.
How Is a NOx Diesel Sensor Cleaned for Mercedes Benz?
Simple NOx sensor cleaning calls for a long soak in a cleaning agent. For three to four hours, you can let them soak in a gasoline injector cleanser. After that, spray the NOx sensor with a carburetor or throttle body cleaning. Since we use carb and choke cleaner to remove carbon from throttle bodies and carburetors, I advise utilizing it.
How Much Does a Mercedes Benz NOx Sensor Replacement Cost?
A NOx sensor's replacement cost varies depending on many factors. Consider if you want brand-new, aftermarket, or original OEM components when determining your spending limit.
The cost is also influenced by the car's manufacture and model. However, NOx for Mercedes-Benz often costs between $250 and $300. High-end sensors, however, might cost between $400 and $800.
Can a Mercedes Benz NOx Sensor Be Repaired?
NOx sensors can malfunction and require repair or replacement, just like any other auto part. When the sensor malfunctions, the car may experience many problems, including poor engine performance, irregular acceleration, low gas mileage, and limp mode.
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If you overlook issues of this nature, things will swiftly deteriorate. You must thus fix the sensor as soon as you can. The lambda probes that measure the nitrogen oxides in exhaust gas are usually the ones that malfunction rather than the sensor.
Do Petrol Driven Mercedes Vehicles Have NOx Sensors?
Because of pollution laws, automakers have known since the 1990s that NOx sensors are needed. The 1990s saw a surge in development, but manufacturers didn't build commercial sensors for a stratified charge, lean-burn gasoline cars with nitrogen oxides absorbers until the early 2000s. The development of NOx sensors by manufacturers is expanded to include urea SCR systems in both light and heavy diesel engines.
What Is the Lifespan of Mercedes NOx Sensors?
Mercedes NOx sensor warranties vary. A NOx sensor may, however, travel 50,000 to 60,000 miles on average. The sensor can survive longer than that with proper care, and it can also break down well before 50,000 miles. Bosch quotes a lifetime of 15,000 hours for its current sensor.
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The Conclusion
A bad NOx sensor is an expensive part, so confirm the fault before you buy one. This guide covered the signs of NOx sensor failure, how to rectify them, and other significant issues. Make sure you are competent enough to perform any repairs on your car before moving on. If not, get assistance from a specialist.