NOx sensorsMercedes-Benz

Mercedes NOx Sensors

NOx sensor faults are common on modern Mercedes diesels and can be tied to AdBlue/SCR efficiency, software, wiring, and driving pattern.

Repair difficulty
Medium
Estimated cost
Medium to high depending on sensor count and coding needs.

Affected models and engines

  • Mercedes diesel and petrol models with NOx monitoring, especially Euro 6 diesel applications

Symptoms

  • Check-engine light
  • AdBlue warning
  • Emissions readiness failure
  • Countdown message

Why it fails

  • Sensors live in high-heat exhaust flow.
  • Wiring, control units, and SCR efficiency can all influence the reading.
  • Cheap generic sensors may not solve the root cause.

Checks before buying

  • Scan actual NOx sensor values and SCR efficiency.
  • Ask whether genuine or coded sensors were installed.
  • Drive until emissions monitors run.
  • Treat cleared codes as unresolved until readiness is complete.

Fault codes to investigate

P20EEP204FU0100

Fault codes guide diagnosis; they do not confirm a part without live data, inspection, service history, and repeat testing.

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