Brake System Internal Leak Test (Two-mode Hybrid)
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
WARNING:
Refer to Brake Fluid Irritant Warning .
CAUTION:
Refer to Brake Fluid Effects on Paint and Electrical Components Caution .
- Ensure is ignition is OFF for at least 60 seconds to allow the system to depressurize and deplete the power reserve.
- Apply the brake pedal several times to verify the power reserve is fully depleted.
- Apply light, steady pressure to the brake pedal. Observe both the brake pedal feel and travel.
- Release the brake pedal.
- If the brake pedal apply felt spongy, but the brake pedal travel was not excessive, perform the following steps:
- Inspect the brake system for external leaks. Refer to Brake System External Leak Inspection .
- Pressure bleed the brake system in order to purge any air that may be trapped in the system. Refer to Hydraulic Brake System Bleeding (Pressure) , Hydraulic Brake System Bleeding (Manual) .
- If the brake pedal apply did not feel spongy, but the brake pedal travel was excessive, perform the following steps:
- Loosen the master cylinder-to-adapter mounting nuts.
- Carefully pull the master cylinder away from the adapter just enough to inspect the mounting surface of the master cylinder.
- Inspect the master cylinder mounting surface at the primary piston (2) for brake fluid leaks.
- If the master cylinder exhibits any leakage around the primary piston (2), then the primary piston primary seal (4) and/or secondary seal (3) is leaking and the master cylinder requires replacement.
- If the master cylinder primary piston (2) does not exhibit any leakage, install the master cylinder to the adapter and pressure bleed the brake system. Refer to Hydraulic Brake System Bleeding (Pressure) , Hydraulic Brake System Bleeding (Manual) .
- If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not excessive, but then gradually fell, then the master cylinder requires replacement due to an internal leak past a piston seal.
- If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not excessive, then fell slightly, then became steady again, then the brake pressure modulator valve (BPMV) may be leaking internally, and may require replacement.