HYDRAULIC PRESSURE CONTROL UNIT, BRAKE SYSTEM, AND DIAGNOSIS METHOD

[Problem] The present invention obtains a hydraulic pressure control unit, a brake system, and a diagnosis method capable of appropriately diagnosing an abnormality of a power supply line. [Means for Resolution] A hydraulic pressure control unit () includes: a hydraulic pressure control mechanism including an inlet valve () as an electromagnetic valve that is electrically connected to a power supply () through a power supply line (), a control device () that controls an operation of the hydraulic pressure control mechanism, and a resistance () that is electrically connected to the power supply () through the power supply line (), in which a diagnosis unit of the control device () performs a power supply line diagnosis in which an abnormality of the power supply line () is diagnosed, in a state where no current is applied to the inlet valve () but a current is applied to the resistance (), based on a voltage change in the power supply line () when the current to be applied to the resistance () is changed.