What the AdBlue injector does
The dosing injector — also called the metering unit, reductant injector or dosing valve — sprays a precisely metered quantity of AdBlue into the exhaust upstream of the SCR catalyst. It is cooled either by coolant or by the AdBlue flow itself, and it purges after shutdown to stop residue baking onto the tip.
Symptoms of a blocked or faulty injector
- Dosing quantity or dosing plausibility fault codes
- NOx conversion faults, because nothing is reaching the catalyst
- AdBlue warning light and inducement countdown
- Pressure build faults, where the pump cannot push through the restriction
- White crystalline deposits visible around the injector body
- Coolant or AdBlue leaks around the injector seal
- Electrical faults — open or short circuit in the injector winding
Cleaning versus replacement — the honest answer
Where crystallisation is light and the injector is still electrically and mechanically sound, cleaning and reseating it can restore correct dosing. We do this where the testing supports it.
But cleaning is not a universal fix, and anyone telling you it is has something to sell. A seized needle, a damaged tip, a failed winding or a heavily baked injector needs replacing. And crucially, if the injector crystallised because of a leaking seal, a failed purge cycle or poor-quality fluid, cleaning it without fixing that cause just resets the clock.
What we test
- Injector winding resistance and electrical control signal
- Actual dosing quantity during a forced dosing routine
- System pressure behaviour with the injector isolated
- Physical condition of the tip, seal and mounting face
- Purge cycle operation, to establish why it blocked in the first place
- Fluid quality in the tank
Diagnosis first. Parts second.
A stored fault code names a circuit, not a culprit. A NOx code can be caused by the sensor, its wiring, a connector full of water, an exhaust leak upstream, poor dosing, or a control module that has lost calibration. Replacing the sensor on the strength of the code alone is how people end up paying twice.
We test live data, dosing behaviour, pressure build, heater circuits and sensor plausibility before recommending any part. If a component genuinely has failed, you will see the evidence for it.
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