Reductant Heater

Keeps reductant liquid in cold weather. The fluid freezes at about −11°C, which is an ordinary winter anywhere with one — so the tank, the supply line, the return line and the metering unit are each heated separately, and the codes for them are lettered A, B, C and D. Which letter is which varies between manufacturers and must be looked up rather than assumed.

The system is only as good as its weakest heater: one frozen section breaks the path from tank to exhaust, and dosing stops as completely as if all four had failed.

Heating is done either by circulating engine coolant through the section via a module-commanded valve, or by an electric element — and the two are diagnosed nothing alike, so establishing which this vehicle uses comes first. Line heaters are typically resistive wire moulded into the hose, which means a failed line heater usually means replacing the whole heated line, and those assemblies are expensive.

Its faults are seasonal and silent. Nothing happens in warm weather; the first hard frost produces a vehicle that cannot dose and an inducement countdown towards refusing to restart. Repair before winter, not during it.

Also known as: adblue heater, def heater, urea tank heater, reductant line heater, scr heater

Referenced by 55 codes

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Codes involving this component (55)

Other components in Exhaust and Emissions

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