Abstract: Apparatuses and methods are provided for detecting contaminant in a fuel system, such as a fuel system of an internal combustion engine. The apparatus includes a fuel filter which includes an upper unit having an inlet port and an outlet port, and a closeable vent. A lower unit is releasably mounted to the upper unit and includes a contaminant collection zone and a contaminant detection sensor made up of a probe and a board with a microprocessor for detecting contaminant collecting in the collection zone within the lower unit. At least one indicator is provided for producing an alarm condition in a response to receiving a signal from the sensor.