Troubleshooting a Low Soft Brake Pedal

Brake bleeding bottle

Several conditions can result in a low spongy brake pedal. Typically, there is air trapped in the brake system. So, first, bleed the brakes to rule out different components and identify the unit or part causing the problem.

Master cylinder

If the brake pedal is still low and spongy, check the pedal free height and isolate the master cylinder by blocking the outlet ports with plugs and checking the brake pedal for firmness. If the pedal is firm, the master cylinder cup seals are good, and the problem exists downstream.

ABS Modulator Valve Assembly

ABS Modulator Valve Assembly

Air can get trapped in the ABS valve modulator, a line or hose, or one of the brake units. When the master cylinder and brake units have no air pockets and the pedal is still low, the hydraulic ABS unit may have an air pocket. Bleed the ABS modulator to remove any air before proceeding to the units.

Swollen Brake Hose

A brake hose.

Inspect the brake system for leaks, repair, and bleed the brakes according to the manufacturer's specifications. The brake hose can rupture internally and swell, resulting in a spongy pedal. The brake hose may require replacement before proceeding with diagnostics.