Abstract: The current through the coil of a solenoid valve is monitored for a deflection which is generated when the valve armature shifts in response to the current being applied to the coil. A lack of detection of the deflection is indicative of a solenoid malfunction and causes generation of an alarm signal.

Abstract: A portion of a solenoid coil melts after a predetermined time period has elapsed to interrupt the flow of current through the coil. The portion which melts can include a reduced cross sectional area which increases the resistance of the portion of the wire. Alternately, a portion of the coil wire can be formed from a material having a higher resistivity than the remainder of the wire.

Abstract: A hydraulic brake system metering valve includes an intergal brake switch having at least one pair of contacts. The brake switch contacts are movable between two positions. The combination valve includes a metering valve assembly having an axially shiftable metering rod. One end of the metering rod is adapted to operate the switch contacts. When pressure is initially applied to the brake system the metering rod shifts, causing the brake switch contacts to move from a first to a second position and thereby generate a first electrical signal. Upon release of the brake pressure, the metering rod shifts back, allowing the brake switch contacts to return to the first position and thereby generate a second electrical signal.