What is the method to test for hydraulic leaks in the brake system?

The correct method to test for hydraulic leaks in the brake system is to pump the brake pedal three times and then hold firm pressure for 5 seconds. This approach allows the driver to assess the integrity of the brake system effectively. When you pump the brake pedal a few times and then maintain pressure, any significant drop in the pedal indicates a potential hydraulic leak. If the pedal sinks slowly (or suddenly) after holding it, that could signal that brake fluid is escaping somewhere in the system, indicating leaks that need to be addressed to ensure safe braking performance.

The other options do not provide an accurate assessment of hydraulic leaks. Pulling the handbrake primarily tests the effectiveness of the parking brake rather than the hydraulic brake system. Visually inspecting the brake fluid level may indicate low fluid but is not a definitive test for leaks. Driving the vehicle at a low speed doesn't allow for a proper check of hydraulic function and could lead to dangerous situations if leaks are present. Therefore, the method of pumping the brake pedal and holding it is the most reliable and practical way to diagnose any issues in the hydraulic brake system.