AdBlue heater fault and tank problems explained
An AdBlue heater fault means the element that thaws and warms the fluid has failed, or its wiring has, so the ECU can't be sure AdBlue will flow in cold weather. On many vehicles the heater, pump and level sensor sit together in the tank, which is why heater and tank faults often show up side by side. Expect an AdBlue warning, a code such as P20B9 and, before long, a restart countdown.
Why AdBlue needs a heater
AdBlue is a mix of urea and purified water that freezes at around minus 11°C. Frozen fluid can't be pumped, so the tank, and on many vehicles the lines, have heaters that thaw it after a cold start.
Because the system has to work in all weather, the ECU checks the heater circuit every time. If the heater fails that check, a fault is stored even in summer.
Signs of a heater or tank fault
- AdBlue warning light on with a full tank
- A "check AdBlue system" or emission system fault message
- Warnings that appear on frosty mornings and fade later in the day
- Level readings that jump about or never change after a top-up
- A countdown to no-restart that a top-up won't clear
- Codes like P20B9, P20BA or P203F
AdBlue crystallisation
When AdBlue dries out, the water evaporates and leaves white urea crystals behind. They build up around the injector tip, in the lines, at the filler neck and anywhere fluid has leaked or been spilt.
Crystals form faster when the exhaust runs cool, which is common on vehicles that do lots of short trips. A blocked injector can't spray properly, so the ECU sees poor NOx readings and logs a fault.
The usual causes
Failed heater element
The heater burns out or goes open circuit. On many Peugeot and Citroen BlueHDi models it's built into the tank, so it can't be swapped on its own.
Wiring and connectors
Road salt and water get into the plugs under the vehicle, and corrosion there can look exactly like a failed heater.
Level or quality sensor
A sensor in the tank that misreads the level or urea content sets codes such as P207F and keeps the light on.
Blocked injector
Crystal build-up stops the injector spraying evenly, which often leads to P20EE further down the line.
Freeze damage
Fluid that freezes in a part without heating can split it, especially in a pump or line that's already worn.
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Cleaning the injector or replacing the tank
AdBlue injector cleaning can get a crusted injector spraying again, but crystals often come back if the exhaust keeps running cool or a leak isn't fixed. It's a fix for the symptom, so it pays to know why the deposits formed.
Where the heater or sensor is built into the tank, AdBlue tank replacement is usually the dealer's answer. The cost depends on the make and whether the tank comes with the pump, so ask for a written quote that includes labour and any coding.
Keeping heater and tank problems at bay
Not every fault can be avoided, but a few habits cut the risk of crystals and sensor trouble.
- Use AdBlue marked ISO 22241 from a sealed container or a pump
- Keep the filler cap closed and wipe up any spills around the neck
- Don't store opened AdBlue for months, as it degrades in heat and sunlight
- Give the vehicle a longer run now and then if it mostly does short trips
- Get warnings checked early, before a countdown starts
What we do and don't do
SGR don't replace AdBlue heaters, tanks, sensors or injectors. What we can do is come out, read the codes and live data, and tell you whether it's the heater, the wiring, a sensor or crystals, for £100 + VAT.
Our AdBlue delete (£330 + VAT) switches the system off in the ECU, so a failed heater no longer brings on warnings.
Does an AdBlue heater fault only happen in winter?
The fault can be stored any time of year, because the ECU tests the heater circuit on every start. Symptoms are often worse in cold weather.
Can I keep using the vehicle with an AdBlue heater fault?
Usually, until a countdown starts. Once it does, the mileage on the dash is how far you can go before the engine won't restart.
Can crystallised AdBlue be cleaned off?
Deposits can be dissolved with warm water and removed from the injector, but it's a temporary fix if the cause isn't dealt with.
What causes an AdBlue level sensor fault?
Wear, corrosion in the connector, crystals on the sensor or contaminated fluid. On tanks with built-in sensors, a fault often means the whole unit is replaced.
Can the AdBlue system be deleted instead of replacing the tank?
Only on a vehicle used off-road or being exported, as those are the only uses we carry out AdBlue deletes for. Our guide on whether an AdBlue delete is legal explains why.
Get a heater or tank fault pinned down
Book a mobile diagnostic and we'll find out whether you're dealing with a heater, a sensor or crystal build-up before you spend on parts. If you'd like an AdBlue delete, we can carry it out on the same visit.
Eccles, Manchester M30 0SF