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Mercedes AdBlue and NOx sensor faults
An AdBlue warning with a countdown on a Mercedes is stressful, because when it reaches zero the engine will not restart. We diagnose the AdBlue system properly and get the countdown cleared. Call us to book as soon as the warning appears.
Why book with us
Mercedes AdBlue and NOx sensor faults with clear advice.
Mercedes BlueTEC and later diesels, including the C-Class, E-Class, GLC, Sprinter and Vito, use AdBlue to cut nitrogen oxide emissions. AdBlue is injected into the exhaust, where it reacts in a catalyst known as the SCR system. Sensors before and after the catalyst check that it is working.
When the system detects a fault, it starts a countdown on the dash, usually a set number of miles until the engine will no longer restart. The law requires this, so it cannot simply be switched off. Topping up the AdBlue only clears it if the tank was genuinely low. If the tank is full and the warning is still there, something has failed.
The common causes on Mercedes diesels are failed NOx sensors, faults with the heater inside the AdBlue tank, a failed AdBlue pump or level sensor, crystallised AdBlue blocking the injector, and contaminated fluid. Each needs a different repair, and some of the parts are expensive, so reading the fault codes is only the start.
We check the fault memory, the live readings from the NOx sensors and the AdBlue quality, and test the pump, heater and injector. Once the repair is done we reset the system and confirm the countdown has cleared, so you can drive with confidence again.
Cars and vans
C-Class, E-Class, GLC, Sprinter and Vito BlueTEC and later diesels.
Countdown cleared
We fix the cause and confirm the no-restart countdown has gone.
NOx sensors tested
Live readings checked so we only replace a sensor that has actually failed.
Book early
Call us to book while there are still miles on the countdown.
Mercedes AdBlue and NOx sensor faults
Our AdBlue fault diagnosis covers
Clear expectations, no surprises. If anything extra is needed, we explain it first.
- Fault code read across the engine and emissions control units.
- NOx sensor live data check before and after the SCR catalyst.
- AdBlue quality and contamination test.
- Tank heater, pump and level sensor testing.
- AdBlue injector inspection for crystal build-up.
- System reset and countdown check after repair.
Mercedes AdBlue and NOx sensor faults
Common questions
- I filled the AdBlue and the warning is still on. Why?
- If the tank was not low, the warning is caused by a fault in the system, often a NOx sensor, the tank heater or the pump. Topping up will not clear it. Call us to book a diagnosis before the countdown runs out.
- What happens when the countdown reaches zero?
- The engine will keep running, but once you switch off it will not restart until the fault is repaired. If you are close to zero, let us know when you call and we will advise on getting it to us.
- Can the AdBlue system be removed?
- No. Removing or disabling emissions equipment is illegal on road vehicles and will fail the MOT. We repair the system so it works as designed.
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Serving drivers across the local area
We provide mercedes adblue and nox sensor faults for customers from across the region — book online or call us.
Experts in mercedes adblue and nox sensor faults
Tell us your car and symptoms, we will advise honestly.
Serving Oldbury, West Midlands and surrounding areas towns. Message or call and we will outline likely costs before we book you in.