Exhaust & emissions · Sant Andreu
AdBlue system: faults and repair
An AdBlue warning that will not clear, a start countdown, or a full tank the car refuses to recognise. We repair the urea system of modern diesels before the car refuses to start.
What does this service include at Tallers Marathon?
Diagnosis of the urea circuit: injector, pump, level and quality sensors, and cleaning of crystallisation.
- Circuit diagnosisPump, injector, level and quality sensors, and tank heaters.
- Crystallisation cleaningCrystallised urea blocks injector and lines: cleaned or replaced.
- Sensors and modulesReplacement of failed level/quality sensors — the no.1 cause of warnings with a full tank.
- Correct resetAfter repair, the system is verified and the start counter restored.
Why is the AdBlue warning on if the tank is full?
Almost always a failed level or quality sensor, or crystallised urea in the circuit. The warning does not distinguish: for the car, "I cannot read the level" and "there is no AdBlue" end the same way — a regulatory engine-start block.
Worth knowing: the AdBlue start block is not a malfunction, it is a legal obligation under emissions rules — the manufacturer cannot let the car run without the system operational. So take the start countdown seriously: when it reaches zero, the car will not start even with a tow truck waiting. On prevention, two counter tips: use branded AdBlue from a sealed container (urea degraded by sun or time trips the quality sensor) and avoid topping up "a litre at a time", which encourages crystallisation at the tank neck.
Frequently asked questions
How many starts do I have left after the first warning?
It depends on the manufacturer: typically the warning starts with margin (a few hundred km or dozens of starts) and grows more insistent. The dashboard shows the exact countdown.
Can I disable the AdBlue system?
No: it is illegal, an ITV failure and carries serious fines. What we do is repair it — usually cheaper than feared.
Which AdBlue should I buy?
Any recognised brand meeting ISO 22241, in a sealed container not baked in the sun. Degraded AdBlue is a direct cause of quality sensor faults.
Does AdBlue freeze or expire?
It freezes below -11 °C (the car manages that with heaters) and degrades with heat and time: do not hoard open containers from one year to the next.
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