رله گرمکن محلول اوره خراب

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.