How It Works: NOx Sensor
|
A NOx sensor detects nitrogen oxides (NO and NO₂) in the exhaust stream of diesel engines. These gases contribute to smog, acid rain, and respiratory issues. The sensor helps monitor and control emissions by feeding real-time data to the engine control unit (ECU), which adjusts fuel injection, exhaust gas recirculation (EGR), and aftertreatment systems like Selective Catalytic Reduction (SCR).
In diesel vehicles with Selective Catalytic Reduction (SCR) systems, NOx sensors are used to determine the amount of DEF (Diesel Exhaust Fluid) needed to reduce NOx emissions. They are typically located before and after the SCR catalyst
|
|
Each NOx sensor operates with two chambers:
- First Chamber: Measures and regulates oxygen levels to avoid interference.
- Second Chamber: Breaks down NOx into nitrogen and oxygen; the oxygen is measured to determine NOx concentration.
Common Reasons for Failure:
Signs of a Faulty Nox Sensor:
Nox Sensors and New EPA Standards for Heavy Duty Vehicles
The EPA’s Clean Trucks Plan introduces the strongest-ever national standards for heavy-duty vehicle emissions starting with Model Year 2027. These rules aim to cut nitrogen oxide (NOx) emissions by over 80%, extending vehicle emission warranties and useful life significantly. With this shift, NOx sensors will become a critical component in meeting compliance—and diagnostics and maintenance of Nox sensors will need to be a core skill for technicians.
- High Exhaust Temperatures: Nox sensors are sensitive to heat and can degrade when exposed to extreme temperatures, especially over loaded heavy duty trucks.
- Soot and Contaminant Buildup: Soot, oil residue, and other particulates can coat the sensor, obstructing accurate readings. Some engine additives can also leave damaging residue on these sensors.
- Electrical Issues: Burnt or damaged wiring harnesses and connectors can mimic sensor failure or cause intermittent faults.
Signs of a Faulty Nox Sensor:
- Check Engine Light
- Poor Fuel Economy
- Rough or Erratic Idling
- Engine Misfires
- Reduced Engine Power or Acceleration
- Soot Buildup and Failed Emissions Tests
Nox Sensors and New EPA Standards for Heavy Duty Vehicles
The EPA’s Clean Trucks Plan introduces the strongest-ever national standards for heavy-duty vehicle emissions starting with Model Year 2027. These rules aim to cut nitrogen oxide (NOx) emissions by over 80%, extending vehicle emission warranties and useful life significantly. With this shift, NOx sensors will become a critical component in meeting compliance—and diagnostics and maintenance of Nox sensors will need to be a core skill for technicians.
|
|
Click "Download File" for the PDF version.
| gpd_tech_tip_255_-_nox_sensors_how_it_works.pdf |
