What is a common sign of brake system malfunction?

A soft or spongy brake pedal is a common sign of a brake system malfunction because it indicates that there may be air in the brake lines, which can compromise the hydraulic pressure needed for effective braking. When the brake pedal feels soft or does not engage firmly, it usually suggests that the brake fluid is not being properly transmitted through the system, potentially due to leaks, insufficient brake fluid, or failing components. This reduces the effectiveness of the brakes and can lead to longer stopping distances, creating a significant safety hazard.

The other options represent symptoms that could also indicate brake issues but are not as broadly recognized as initial signs of malfunction. A loud grinding noise when braking typically suggests worn brake pads and might indicate a more severe level of wear, while illuminated brake lights can indicate issues with the brake light switch or electrical system. Similarly, shaking in the steering wheel during braking often points to warped brake rotors or issues with the suspension, rather than the immediate hydraulic pressure concerns indicated by a soft pedal.