Just in case anyone wonders what it is (I had no idea)
Reductant Heater & Sender Assembly
The reductant heater and sender assembly contains pickup tube for reductant pump module, an electric heating element, a reductant temperature sensor and an electrode type level sensor. The heating element is directly above pickup tubes inlet filter. When reductant temperature sensor detects the diesel exhaust fluid temperature dropping to the freezing point of 12°F (-11°C), the PCM will command the glow plug control module to provide voltage to heating element. The heating element thaws liquid reductant within reductant heater and sender assembly reservoir during cold ambient temperatures.
The reductant level sensor incorporates four stainless steel electrodes, with three electrodes arranged vertically to provide a high, middle, and low level signal. The fourth electrode acts as a ground. When reductant tank is full, DEF closes a circuit between all three level electrodes and ground electrode, indicating tank is full. As DEF is consumed, level drops and uncovers each electrode in sequence. The PCM calculates DEF level based on these signals
Reductant Heaters
The reductant heaters maintain DEF in a liquid state during cold ambient temperatures. There are three heating elements in system, each receiving voltage from the glow plug control module. The reductant tank heater is integral to reductant heater and sender assembly. The reductant pump heater is integral to reductant pump assembly
Looks like they're about $259 on fleabay
