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Difficulty: MediumABS and Electronic Stability

You are making an emergency stop in a vehicle fitted with an anti-lock braking system (ABS). As you brake heavily, you feel the brake pedal rapidly pulsing and vibrating under your foot. What action should you take?

  1. A
    Release the brake pedal and pump it rapidly until steering control is restored
  2. Maintain firm, continuous pressure on the brake pedal until the vehicle comes to a complete stopAnswer
  3. C
    Ease off the brake pedal slightly to stop the vibration and prevent wheel lock-up
  4. D
    Apply the handbrake immediately and disengage the clutch to assist braking

Answer

Maintain firm, continuous pressure on the brake pedal until the vehicle comes to a complete stop.
Rapid pulsation and mechanical noise through the brake pedal are normal signs that the anti-lock braking system (ABS) is operating correctly. When wheel speed sensors detect an impending lock-up, the hydraulic control unit rapidly releases and reapplies brake pressure many times per second. To achieve maximum deceleration while retaining steering control, the driver must keep pressing the footbrake down hard and continuously until the vehicle comes to a halt.

Step-by-Step Solution

1
Identify the cause of the brake pedal vibration
Recognise that rapid pedal pulsation is the normal physical feedback of an activating anti-lock braking system (ABS).
The ABS hydraulic modulator cycles brake pressure rapidly to prevent wheels from locking under heavy braking.
2
Determine the correct driver response during ABS activation
Keep the foot pressed firmly and continuously on the brake pedal while steering as needed.
The system cannot automatically modulate braking force to maintain tyre grip and steerability if the driver eases off or pumps the pedal.

Key Concept

Driver operation and pedal feedback during anti-lock braking system (ABS) activation
Estimated Time:1m 0s
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Topics

ABS and Electronic Stability

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