An engine unit including a heater provided in a blow-by gas returning path for returning a blow-by gas that leaks out from a combustion chamber of an engine to an intake path. The heater is electrically connected to a controller of the engine through wiring harnesses. The controller is configured to, while controlling energization of the heater, perform an abnormality detection on the wiring harness based on a magnitude of current flowing to the wiring harness during energization of the heater, and perform an abnormality detection on the heater and the wiring harnesses based on a magnitude of voltage applied to the wiring harness located downstream from the heater during non-energization of the heater.