Vehicle brake system

A vehicle, comprising:

• a vehicle body;
• a plurality of wheels supported by the vehicle body;
• a plurality of brakes operatively coupled to the wheels to control speeds of the wheels;
• a hydraulic fluid source in fluid communication with the brakes;
• and
• a computer having a processor and a memory storing instructions executable by the processor to:
• determine the vehicle is in a park mode;
• in response to determining the vehicle is in the park mode, actuate the hydraulic fluid source to provide hydraulic fluid at a volumetric rate to one of the brakes,
• while providing hydraulic fluid at the volumetric rate to the one of the brakes, detect pressures of the one or more of the brakes;
• and
• based on the volumetric rate to the one of the brakes and the pressures of the one or more of the brakes, determine a volume-pressure curve defining brake pressure as a function of hydraulic fluid volume delivered to the one of the brakes.

A method, comprising:

• determining that speeds of wheels of a vehicle are zero;
• after determining the speeds of the wheels are zero, actuating a hydraulic fluid source to provide hydraulic fluid to a first set of one or more of the brakes at a first pressure sufficient to maintain the vehicle body at a present position and to provide hydraulic fluid at a volumetric rate to one or more of the brakes not in the first set;
• while providing hydraulic fluid at the volumetric rate to a brake not in the first set, detecting second pressures of the brake not in the first set;
• based on the volumetric rate to the brake not in the first set and the second pressures of the brake not in the first set, determining a volume-pressure curve for the brake not in the first set;
• and
• actuating the brake not in the first set based on the volume-pressure curve.