Woke up to a frozen AdBlue warning on your dash? You’re not alone. When temperatures in Stoke-on-Trent drop below -11°C, the AdBlue in your tank, pump and lines can freeze solid, triggering countdown warnings and preventing your van from starting. The good news? Modern systems are designed to handle frost, and most frozen AdBlue issues fix themselves once the engine warms up. But if you’re parked outdoors overnight or storing AdBlue bottles in an unheated garage, you need to know the freezing point, how to defrost safely, and when a frozen system needs professional help.
What is the freezing point of AdBlue?
AdBlue freezes at -11°C (12°F). That’s the temperature at which the 32.5% urea solution in AdBlue starts to crystallise and turn into slush. At -15°C and below, it becomes solid ice.
For context, Stoke-on-Trent typically sees winter lows of -2°C to -5°C, but during cold snaps (like January 2024), temperatures can drop to -8°C to -12°C overnight, especially in Biddulph, Leek and rural areas around the Moorlands. If your van is parked outside without engine heat, the AdBlue tank can freeze.
What happens when AdBlue freezes?
- The AdBlue pump can’t draw fluid from the tank
- The dosing injector stops spraying AdBlue into the exhaust
- The SCR system detects low AdBlue flow and triggers a countdown warning
- If the system stays frozen, you’ll see “AdBlue system fault – engine start prevented in 500 miles”
But here’s the key: modern AdBlue systems have built-in heaters in the tank, pump and lines. Once you start the engine and it warms up (usually 10–15 minutes of idling or driving), the heaters defrost the AdBlue automatically and the system resets.
Will my van start if the AdBlue is frozen?
Yes – in most cases. If the AdBlue froze overnight but the tank still has fluid and no fault codes are stored, your van will start normally. The engine doesn’t need AdBlue to start, only to keep running long-term and meet emissions limits.
When you might have a problem:
- If the AdBlue tank was already low before it froze, the system may have logged a “low level” fault and started the countdown. Frozen AdBlue makes the level sensor read incorrectly, so the ECU thinks the tank is empty.
- If the AdBlue heater has failed (fault code P13DF or P20E9), the system won’t defrost and you’ll be stuck with a countdown warning.
- If you’ve already hit the countdown limit (0 miles remaining), the ECU will prevent the engine from restarting even if the AdBlue defrosts.
In these cases, you’ll need a mobile AdBlue repair service to top up the tank, reset the countdown and check the heater circuit.
How to defrost frozen AdBlue in your van
If you’ve got a frozen AdBlue warning on the dash, follow these steps:
1. Start the engine and let it idle
The AdBlue heater is powered by the engine, so the first step is to start the van and let it idle for 10–15 minutes. Don’t rev the engine – just let it warm up naturally. The heater will defrost the tank, pump and lines automatically.
2. Drive gently for 10–15 minutes
Once the engine is warm, drive normally for 10–15 minutes. This circulates warm coolant through the AdBlue heater and speeds up defrosting. Avoid short trips – the system needs sustained heat to fully defrost.
3. Check the warning light
After 15–20 minutes of driving, check the dash. If the AdBlue warning light has gone off and the countdown has reset, the system has defrosted successfully. If the light stays on, see the troubleshooting section below.
4. Top up if the tank was low
If the tank was below quarter-full before it froze, the level sensor may have logged a fault. Top up with 5–10 litres of fresh AdBlue (make sure the bottle isn’t frozen – bring it indoors overnight if it’s been stored in a cold garage). The system should reset within 30 seconds of restarting the engine.
Never try to force-defrost AdBlue by:
- Pouring hot water on the tank (thermal shock can crack plastic tanks)
- Using a heat gun or blowtorch (fire risk and tank damage)
- Adding antifreeze or other chemicals to the AdBlue (contaminates the system and triggers P20EE faults)
How to store AdBlue bottles in winter
If you keep spare AdBlue bottles in your van, garage or shed, they can freeze just like the tank. Frozen AdBlue in a sealed bottle is safe – it won’t damage the container – but you can’t pour it until it defrosts, and repeated freeze-thaw cycles can degrade the urea concentration over time.
Winter storage tips:
- Store indoors above 0°C – a heated garage, utility room or under-stairs cupboard is ideal.
- Keep bottles sealed – exposure to air and moisture contaminates AdBlue and reduces its effectiveness.
- Don’t store in direct sunlight – UV light degrades urea. Keep bottles in a dark, cool (but not freezing) place.
- Check expiry dates – AdBlue has a shelf life of 12–18 months. Old or contaminated fluid triggers P20EE and P204F faults.
If you’ve got a frozen bottle, bring it indoors and let it defrost naturally at room temperature (15–20°C). Don’t microwave it or put it near a radiator – rapid heating can cause the bottle to expand and split.
What if the AdBlue warning won’t clear after defrosting?
If you’ve followed the defrost steps above and the warning light is still on after 20–30 minutes of driving, you likely have one of these faults:
AdBlue heater failure (P13DF, P20E9)
The heater element in the tank or pump has failed, so the system can’t defrost. You’ll need a replacement heater and a fault code reset. Our same-day mobile service can diagnose and fix heater faults on-site in Stoke-on-Trent, Newcastle-under-Lyme and surrounding areas.
Low AdBlue level (P20EE, P204F)
The tank was low before it froze, and the level sensor has logged a fault. Top up with 5–10 litres and restart the engine. If the light stays on, the sensor may need cleaning or replacement.
AdBlue pump fault (P20E8)
Repeated freeze-thaw cycles can damage the pump seals, causing low pressure. You’ll need a pump replacement or, in some cases, an AdBlue system removal if the repair cost is too high.
For a full breakdown of AdBlue fault codes, see our Mercedes Sprinter fault code guide or top AdBlue fault codes page.
“Left my Sprinter parked outside in Biddulph overnight during the January cold snap – minus 10°C,” Mark the builder told me. “Woke up to a red AdBlue warning and 300 miles to empty. Started the engine, let it idle for 15 minutes while I had breakfast, and by the time I’d driven to the first job in Hanley, the light was off. The heater did its job – no call-out needed.”
AdBlue Freezing FAQ
At what temperature does AdBlue freeze?
AdBlue freezes at -11°C (12°F). At this temperature it turns to slush, and at -15°C it becomes solid ice. Modern vans have heated AdBlue tanks that defrost the fluid automatically once the engine starts.
Can I drive with frozen AdBlue?
Yes, but only if the engine starts and the AdBlue system hasn’t triggered a countdown warning. Once you start driving, the engine heat will defrost the AdBlue within 10–15 minutes. If the warning light stays on after 20 minutes of driving, you may have a heater fault or low level issue.
Will frozen AdBlue damage my van?
No – AdBlue expands slightly when it freezes, but modern tanks are designed to handle this without cracking. The built-in heater defrosts the fluid safely. However, repeated freeze-thaw cycles can damage pump seals and sensors over time, especially if the AdBlue is contaminated or old.
How do I prevent AdBlue from freezing?
You can’t prevent AdBlue from freezing in extreme cold, but you can minimise problems by: keeping the tank above half-full (less air = slower freezing), parking indoors or in a sheltered spot when possible, and running the engine for 10–15 minutes before setting off on cold mornings to activate the heater.
Can I add antifreeze to AdBlue?
No – never add anything to AdBlue. It must remain pure ISO 22241 urea solution. Adding antifreeze, water, diesel or any other chemical will contaminate the system, trigger P20EE and P204F faults, and require a full tank flush and sensor replacement. If your AdBlue keeps freezing due to a heater fault, call a mobile specialist instead.
What if my AdBlue bottles are frozen?
Bring them indoors and let them defrost naturally at room temperature (15–20°C). Don’t pour frozen AdBlue into your tank – it won’t flow properly and can cause air pockets. Once defrosted, shake the bottle gently and check for sediment or discolouration before using.
AdBlue warning won’t clear after defrosting?
We diagnose and fix AdBlue heater faults, pump failures and sensor issues on-site across Stoke-on-Trent, Newcastle-under-Lyme, Stafford and Crewe.
07503 134 362 |
✉ info@adbluespecialist.co.uk
Hours: Mon–Sun 09:00–20:00
