Cause
Failed reductant heater relay
The relay powering a reductant tank or line heater, failed. The fluid freezes at around minus eleven degrees, so the heaters are what keep the system usable in winter — and they draw enough current to need a relay rather than a module output.
Failed open, the heaters never run and the system is inoperable in cold weather: frozen fluid, no dosing, and the inducement sequence beginning. The fault is entirely seasonal, appearing on the first hard frost and absent all summer, which is why it survives a service. Welded closed is the opposite, heating continuously and degrading the fluid until the quality sensor reports it. Substitute an identical relay as a first test, and measure the heater element's resistance if the replacement fails quickly.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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