What Normal AdBlue Consumption Looks Like

Before calling something excessive, it helps to know the baseline. The German automotive industry association VDA, which owns the AdBlue trademark and sets the licensing terms, states that a passenger car consumes an average of around 1.5 litres of AdBlue per 1,000 kilometres, and that consumption varies with vehicle weight and driving style.

Translated into the numbers a UK driver actually uses, that is roughly one litre every 400 miles for a car. Vans sit higher because they are heavier and worked harder, and a fully laden 3.5-tonne panel van doing multi-drop work can comfortably double a car’s rate without anything being wrong.

The useful signal is not the absolute number. It is the change. A van that always went 3,000 miles between top-ups and now goes 800 has a fault, even if 800 miles would be perfectly normal for a different vehicle.

Four Reasons It Is Not a Fault

Plenty of consumption complaints turn out to be the system working exactly as designed. It is worth ruling these out before paying anyone to look.

• Cold weather and short journeys. The SCR catalyst has to reach temperature before dosing is efficient. Winter town work means more dosing for the same result.
• Heavy loads and towing. More engine load produces more raw NOx, and more NOx needs more urea to neutralise. A laden van genuinely uses more.
• Stop-start urban duty cycles. Steady motorway running is the most efficient case; delivery rounds are the least.
• A recent software update. Several manufacturers revised SCR dosing strategies after real-driving-emissions rules tightened, and the revised maps often dose harder than the ones they replaced.

None of those should double consumption overnight. If the change was sudden rather than seasonal, move on to the faults below.

Four Faults That Make a Van Drink AdBlue

1. A NOx sensor reporting badly, but not badly enough to flag

This is the most common cause we see and the most frustrating, because the sensor is not dead. A NOx sensor that has drifted still returns plausible-looking values, so the ECU trusts them. If it over-reports NOx downstream of the catalyst, the ECU concludes that conversion is poor and doses more urea to compensate.

Consumption rises. Emissions do not improve, because the extra urea was never needed. Often no fault code is stored at all, because nothing has gone out of range — it has simply gone wrong.

2. A leaking or partially blocked dosing injector

The dosing injector meters AdBlue into the exhaust stream in precise pulses. A worn seat can weep between pulses, so fluid leaves the tank without ever being counted as a dose. The ECU then doses the amount it thinks is required on top of what has already leaked.

The tell is usually visible rather than electronic: white or pale-yellow crystalline deposits around the injector body or the exhaust boss. We have set out the wider failure pattern in our guide to AdBlue injector failure symptoms and replacement costs.

3. A physical leak from the tank, lines or pump

Less common but far simpler to confirm. AdBlue leaks evaporate and leave a distinctive white residue behind rather than a wet patch, so the evidence survives long after the drip has dried. Look under the tank, along the delivery line and around the pump housing.

Pump-side leaks often arrive alongside pressure faults rather than on their own, and the two get confused constantly. Our breakdown of AdBlue pump failure symptoms covers how the pump behaves when it is genuinely at fault.

4. A level sensor that is reading the tank wrong

Worth naming because it produces the appearance of high consumption without any extra fluid being used. If the level sensor under-reads, the gauge falls faster than the tank empties and the driver tops up more often than necessary. The clue is that the tank takes noticeably less fluid than the gauge suggested it should.

Leak or Over-Dosing? How to Tell

The two causes need completely different work, so separating them early saves money. A rough field test costs nothing.

Park the vehicle on clean, dry ground overnight and look underneath in the morning. A leak that only shows when the system is pressurised will not appear, but a tank or line leak usually will.

Why a New NOx Sensor Often Does Not Fix It

This is the part that catches people out, and it is expensive when it does. NOx sensors are not cheap, and fitting one to a van that is over-dosing feels like the obvious move.

The problem is that the ECU holds learned adaptation values built up from the old sensor’s readings. Fit a new sensor and those learned values remain, so the system carries on dosing against a correction it worked out from faulty data. Consumption stays high, the owner concludes the new sensor was faulty too, and a second one goes in.

The adaptation has to be reset and relearned with a tool capable of talking to the SCR system properly. A generic code reader will clear a stored fault but will not touch adaptations. If you want the cost side of the sensor decision first, our guide to NOx sensor replacement costs in the UK sets out what the parts and labour actually run to.

There is a second reason not to reach for parts first. VDA’s guidance notes that running an SCR-equipped vehicle without adequate AdBlue risks damaging the SCR equipment itself, and the ACEA driver guidance is equally clear that the AdBlue tank must not be allowed to run to empty. An owner who is watching a rising bill and starting to stretch the intervals between top-ups is trading a diagnostic problem for a hardware one.

What Diagnosis Actually Involves

Reading stored codes is the least useful part of this job, because over-dosing frequently stores nothing. What matters is live data: upstream and downstream NOx values compared against each other, dosing quantity per unit of time, tank level trend, and the adaptation values the ECU is currently applying.

Those four together will usually separate a drifting sensor from a weeping injector inside half an hour, without removing anything. It is the work our mobile diagnostics service exists to do, and it is why we would rather scan a vehicle than quote for a part over the phone.

If the outcome is a genuine component fault, that is a repair. If the outcome is a system that has learned bad values, it is a software and adaptation job, which is the route we take on most of the AdBlue problems we are called out to.