A method of detecting a leak in a hydraulic trailer brake circuit of a trailer includes providing a controller, a base valve, a first sensor, a second sensor, a control valve having a solenoid, a reduction valve, a hydraulic fluid supply, a first brake output, and a second brake output. The method also includes supplying a first pressure to an inlet of the base valve and outputting a second pressure from an outlet of the base valve to the first brake output. The first pressure is detected by the first sensor and the second pressure is detected by the second sensor, and the detected first and second pressures are communicated to the controller. The difference between the first and second pressures are compared to a threshold, and a leak is detected in the hydraulic trailer brake circuit if the difference satisfies the threshold.