Mercedes-Benz AdBlue Problems
Expert diagnostics for Mercedes-Benz SCR systems. If your Mercedes-Benz has an AdBlue warning, NOx sensor fault, engine derate, or has started a restart countdown, we can help identify the root cause using dealer-level diagnostic equipment.
Common Mercedes-Benz SCR Faults
Mercedes-Benz commercial vehicles use SCR (Selective Catalytic Reduction) systems to meet Euro 5 and Euro 6 emissions standards. NOx sensors, the AdBlue dosing pump, dosing injector, and SCR catalyst are the components most commonly implicated in faults. We diagnose all fault types using dealer-level equipment and live data analysis — not code-reading alone.
NOx Sensor Faults
The upstream and downstream NOx sensors are the most common failure point on Mercedes-Benz trucks. They fail from soot contamination, connector corrosion, and thermal damage. A sensor fault code may also indicate wiring problems or a poorly performing catalyst rather than sensor failure — live data analysis is essential before replacing any part.
Dosing Pump Failures
The AdBlue pump must maintain correct pressure for accurate dosing. Pressure faults can result from pump wear, internal leaks, air ingestion, or blockages. Actuator testing with our diagnostic equipment measures real pump output against the expected value.
Derate & Countdown
Mercedes-Benz trucks implement engine derate and a "starts remaining" countdown when SCR faults reach a critical threshold. The countdown cannot be reset by clearing codes with a generic scanner — proper diagnostic access is required.
Manufacturer Diagnostic Profile
Models covered
Actros · Arocs · Antos · Atego
Engine families
OM471 · OM470 · OM936
Diagnostic equipment
Mercedes-Benz Xentry with SD Connect
Terminology checked
MR engine-management and SCR control-system fault information
Mercedes-Benz STAR diagnostic system
Services
- Complete SCR Diagnostics
- NOx Sensor Testing & Wiring Checks
- AdBlue Pump Pressure Testing
- Dosing Injector Actuator Testing
- Countdown Reset (with fault resolution)
- ECU Software Verification
Vehicle Immobilised?
If your Mercedes-Benz has reached zero restarts, call us directly.
01302 20202907929 765432Fault Codes — Mercedes-Benz truck MR / SCR control / Xentry
Common Mercedes-Benz AdBlue & SCR Fault Codes
Mercedes-Benz SCR codes identify a monitored circuit or system condition. Diagnosis must confirm the fault state, relevant live data and wiring before a component is condemned.
Mercedes-Benz truck fault displays are controller and generation dependent. The codes below are retained from Actros/Atego fault-code material and should be confirmed in Xentry for the actual vehicle.
| Fault code | System | Common description | Possible causes |
|---|---|---|---|
| 1387 / 2 | Reductant pressure sensor | Circuit range/performance | Pressure-sensor data, connector, wiring or actual pressure condition |
| 1761 / 1 | Reductant level | Level low | Fluid level, level-sensor data or circuit concern |
| 3050 / 7 | SCR catalyst | SCR catalyst error | NOx conversion context, dosing, fluid quality, exhaust condition or catalyst performance |
| 4334 / 18 | Reductant pressure | Reductant pressure too low | Pressure-system supply, restriction, leak, pump or pressure data concern |
4334 / 18
Mercedes-Benz 4334 / 18 — reductant pressure too low
What it means
The SCR control system has recorded low reductant pressure. It requires a pressure and delivery diagnosis, not an assumption that the pump alone is at fault.
Common causes
- •Supply restriction or crystallisation
- •Leak or air ingress
- •Pump delivery issue
- •Pressure sensor, wiring or connector condition
Symptoms
AdBlue warning · Engine or emissions warning · Power restriction · Inducement message on affected systems
What ECUFLASH checks
ECUFLASH confirms the fault in Xentry, compares target and actual pressure information, and checks the dosing path and electrical evidence before a repair recommendation.
Source basis: Mercedes-Benz Actros and Atego fault-code material