What does a spongy brake pedal typically indicate?

A spongy brake pedal commonly indicates the presence of air in the brake lines or low brake fluid. When there is air in the brake line system, it can compress more than the brake fluid during braking, leading to a brake pedal that feels soft and spongy when pressed. This is because air is compressible, while brake fluid is not. Additionally, low brake fluid levels can result in a similar feeling. If the brake fluid is below the recommended level, it can mean that there is either a leak in the system or that the brake pads are excessively worn, which would also lead to decreased performance and a spongy pedal feel.

In contrast, the other options present different issues. The presence of water in the brake lines typically leads to corrosion and braking inefficiency, rather than a spongy feel. Low tire pressure affects vehicle handling and tire wear, not the brake pedal feel. Excessive wear on brake pads can lead to a different type of pedal feel, often more of a firm or hard brake pedal as the pads lose material, rather than sponginess. Understanding these distinctions is key in diagnosing braking issues effectively.