What is one indicator of a vehicle's braking system needing maintenance?

A spongy or unresponsive brake pedal is a significant indicator that a vehicle's braking system may require maintenance. When the brake pedal feels spongy, it often suggests that there is air in the brake line, a problem with the brake fluid, or potential issues with the brake components themselves, such as worn brake pads or a failing master cylinder. This condition can lead to decreased braking effectiveness, which is a safety concern that needs immediate attention.

The other indicators mentioned also reflect potential issues, but a spongy or unresponsive pedal is a clear sign of something wrong with the hydraulic system that is critical for effective braking. In contrast, a smooth brake pedal with little resistance might suggest that the brakes are functioning well, while loud grinding noises typically indicate severe wear and tear but might not directly relate to pedal feel. A constantly illuminated braking light indicates a problem that needs checking but does not specify the brake pedal's condition, making it less direct in assessing immediate maintenance needs.