Which component in the hydraulic system activates the brake light when there is a leak?

• A. Master cylinder
• B. Pressure differential valve
• C. Anti-lock brake control module
• D. Brake pedal switch

Answer: (B)

In a hydraulic braking system, the pressure differential valve plays a critical role in monitoring the hydraulic pressure balance between the two circuits of the braking system. When a leak occurs in one of the brake lines, this valve detects the change in pressure and activates a warning system, which can include turning on the brake light. This serves as an alert to the driver that there is a problem within the braking system that requires immediate attention.

The master cylinder generates hydraulic pressure, but it does not activate the brake light directly in response to a leak. Similarly, the anti-lock brake control module manages the ABS functionality but does not engage the brake light for leak detection. The brake pedal switch is responsible for activating the brake lights when the pedal is pressed but is not designed to respond to changes in hydraulic pressure caused by a leak. Thus, the pressure differential valve is the component specifically tasked with signaling any imbalances, including those due to leaks, making it the correct answer for this question.