AdBlue warning light: low level, bad fluid or a fault?

Which warning have you got, and what to do

• Low level: a message to refill or top up AdBlue, often with a range in miles. Top up with AdBlue that meets ISO 22241, never water or additives. This is the only warning a top-up fixes.
• Quality: a message about incorrect or poor-quality AdBlue. It can mean diluted or contaminated fluid, but the rules let makers judge quality from NOx sensor readings, so a sensor or dosing fault can bring up the same message. Don't keep topping up and driving. Under the rules for cars and vans, if it isn't put right within 50 km (about 30 miles), restrictions such as a no-start countdown can begin.
• System fault: a message about an AdBlue, SCR or emissions fault, sometimes with the engine management light. Something in the system has failed or is reading out of range. If dosing has stopped, the same 30-mile rule applies, so note the message and any mileage shown and get the codes read soon.
• Countdown: miles or starts remaining. Treat it as urgent, book the repair while it still starts, and avoid switching off anywhere you can't leave the vehicle.

A code reader confirms which it is. Generic codes include P203F (reductant level too low) and P207F (reductant quality performance), though manufacturer software can word them differently.

Amber, red or flashing: what it tells you

• Steady amber with a range shown: usually the early low-level stage. Top up soon. If the message mentions a fault, book it in.
• Flashing, red, chimes or a countdown: the warning has escalated and the vehicle is heading for a speed or power limit or a no-start, depending on the model.
• AdBlue light plus engine management light: this points to a stored emissions fault, not just a low tank.

AdBlue light on after filling

• It hasn't registered yet. Some vehicles only update the level after the ignition has been on for a while or after a short drive. Your handbook gives the procedure.
• Not enough went in. Once restarts are blocked, the rules don't let the block lift until the fault is fixed or a minimum amount has gone in: at least 10 per cent of the tank, or enough to last one and a half tanks of diesel, depending on the system. If the tank ran dry, a small bottle may not do it.
• The level sender has failed. If the gauge or range doesn't change after a proper fill, suspect the sender. On some vans it is part of a combined tank unit with the pump and heater.
• It wasn't only a level warning. A quality or system fault can sit alongside a low level, so filling up clears one warning and leaves the other.

When topping up won't fix it

• NOx sensors before and after the SCR catalyst.
• The dosing pump, or an AdBlue injector blocked by urea crystals.
• Tank and line heaters. AdBlue freezes at about minus 11°C, so a heater fault can show up first on a cold morning.
• The level or quality sensor in the tank.
• Wiring and connectors under the vehicle, exposed to road spray and exhaust heat.
• Contaminated fluid, which means draining and cleaning the system.
• Engine-side faults, such as EGR problems, that change how much NOx the SCR system has to deal with.

Why the light comes back after a reset or a cheap sensor

We diagnose before fitting parts, then confirm the repair on a drive with live data, so the fault is fixed rather than just cleared.

What affects the cost

• Which fault it is: a level sender is a different job from a NOx sensor or a dosing pump.
• Whether the part is replaced on its own or is built into a combined tank unit, as on some vans.
• Whether the system is contaminated and needs draining and cleaning.
• Whether new parts need coding or adaptation after fitting.
• Whether the vehicle still drives or is already in a no-start, and where it is.

We don't put AdBlue repair prices online because the same warning can mean very different repairs. Call with your reg and the warning message and we'll quote for your vehicle. How we quote

Related