P203F: Reductant Level Too Low
What to do
Fill the reductant tank with the correct fluid, from a sealed container, as soon as you reasonably can. It is sold at fuel stations and motor factors under names like AdBlue or DEF, and it is inexpensive.
Do not put anything else in it — not water, not screenwash. The vehicle measures the fluid's quality and the wrong liquid means draining the tank, which is a real bill.
Do not leave it until the car stops. The countdown ends in the engine refusing to restart, and filling the tank at that point does not always start it straight away — many vehicles need a drive cycle to check the system first, which is a very awkward place to discover that.
If you have just filled it and the warning stayed on, say so. That points at the level sensor or a leak instead, and looking underneath for white crystalline deposits is worth doing.
What this code means
The reductant tank is nearly empty.
This is the most straightforward code in the family and usually the cheapest to resolve: the tank needs filling. It is worth stating plainly, because a driver seeing a warning light and a fault code often assumes something has broken.
What matters is what happens if it is not filled, and that sequence is legally mandated rather than a manufacturer's choice. A diesel that cannot reduce its nitrogen oxide output must make itself progressively unusable. The stages escalate over hundreds of miles: a warning, then a message with a countdown, then a speed limit, then a refusal to restart once the engine is switched off.
The countdown is generous and it does not pause. Drivers routinely ignore the first warnings for weeks and then discover the vehicle will not start in a supermarket car park. Filling the tank at that point does not always start it immediately — many vehicles need a drive cycle to verify the system before the lockout lifts.
Fill it with the correct fluid from a sealed container. Reductant is a precise 32.5% urea solution; water, screenwash or anything else ruins the system, and the vehicle can detect the difference.
If the tank was recently filled and this code appeared anyway, the level sensor or a leak is the real fault — look under the vehicle for white crystalline deposits.
Likely causes
Start here
Less common
- Faulty reductant level sensor · moderate
- Reductant leak from tank or lines · moderate
- Stuck sensor float · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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