Re-mapping5 min read
AdBlue warning light: what it means and how urgent it is
An AdBlue warning that counts down to a no-start looks alarming. It is usually a sensor, an injector or a heater rather than the tank — and it is fixable without a delete.
By Kaine Carter
AdBlue is a fluid injected into the exhaust of most diesels from about 2015 onwards. It reacts with the exhaust gases in a part called the SCR system to cut harmful emissions. Because those limits are a legal requirement, the car is designed to stop you driving indefinitely with the system not working.
First: is it just low?
The simplest version of the warning means the tank is running low. Top it up with AdBlue to the ISO 22241 standard — sold at most fuel stations — through the blue filler, usually next to the fuel cap or in the boot. Some cars need a short drive, or the ignition cycling a few times, before the warning clears.
When topping up does not clear it
If the tank is full and the warning stays, or it says there is a system fault, something in the system has failed. The common causes are specific and repairable:
- A quality sensor that has drifted and is misreading the fluid.
- A dosing injector crystallised shut, which can often be cleaned rather than replaced.
- A failed tank heater, so the fluid freezes in cold weather.
- A pump that has lost pressure.
- A NOx sensor reading out of range at one end of the system.
How urgent is the countdown?
Urgent enough to book now rather than next month, but not a reason to panic. The countdown is real — at zero the engine will not restart — but it runs in hundreds of miles, and the fault behind it is usually a day's work. Make a note of the figure on the dash when you call.
Why a delete is not the answer
You will find people offering to delete or emulate the system. On a road vehicle that is illegal, it fails the MOT, it can invalidate your insurance, and it is the emissions tampering the DVSA has been most active against. We repair the system rather than remove it.
How we fix it
We diagnose before we quote: live data from the SCR system, pressure tests, and the sensors checked against what the exhaust is actually doing. Then you get a written figure for the repair that is actually needed. AdBlue diagnosis and repair starts from £249, with parts priced separately once the fault is found, and the work is done at your address in Milton Keynes, Leighton Buzzard, Bedford, Buckingham and Northampton.
