P24FF: Reductant Temperature Too High
What to do
Get this looked at reasonably promptly, because the fluid itself is being spoiled while the fault continues. Overheated reductant loses its effectiveness and leaves deposits that block the injector — so a delay here turns a sensor or relay repair into a larger one.
Mention whether the fault appears in hot weather or all year round. A tank heater stuck on is the commonest cause, and it usually shows itself in summer.
Expect the tank to need draining and refilling if the fluid has been overheated for a while. That is normal and not a sign of being oversold.
The car will drive normally for now, but the emissions system escalates if left, moving towards a speed limit and eventually a restart lockout.
What this code means
The reductant fluid has exceeded the temperature at which it remains stable.
This fluid is temperature-sensitive at both ends, and that shapes the whole system around it. It freezes at about −11°C, which is why the tank and lines are heated. And it degrades when hot — above roughly 70°C the urea in it begins to break down in the tank, losing potency and leaving deposits behind.
So the system actively cools it, usually by circulating fluid back to the tank and by choosing when to dose. This code says that protection has failed or been overwhelmed.
The causes divide cleanly into three groups.
- The tank heater is stuck on. It is meant to run only in cold weather; a failed relay or a shorted control circuit leaves it heating in summer, which is the classic cause.
- Cooling flow has stopped — a blocked return line, a failed pump, or air in the circuit.
- The sensor is wrong, reporting a temperature the fluid never reached.
Overheated fluid does lasting harm rather than transient harm. Degraded reductant cannot reduce NOx properly, so expect efficiency and dosing codes to follow — and the deposits it leaves are what crystallise injectors shut.
Check the heater circuit first, because a heater running when it should not is both the most common cause and the one that keeps damaging fluid until it is found.
Likely causes
Start here
- Reductant tank heater stuck on · moderate
- Faulty reductant temperature sensor · moderate
Less common
- Blocked reductant return line · moderate
- Reductant diluted or incorrect fluid · moderate
- Wiring shorted to voltage · 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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