C055D: Brake Hydraulic Circuit B Leak

What it means

Brake Hydraulic Circuit B Leak: a leak has been detected in this brake-hydraulic circuit, which reduces braking pressure. Safety-critical.

At a glance

• Usually lights the ABS or stability-control warning light
• The engine or gearbox may go into limp mode

How it works

Brake hydraulic circuit B carries pressurised brake fluid as part of the vehicle’s braking system. This code indicates that pressure or fluid loss points to a leak in circuit B, which can reduce braking force and alter pedal feel.

Common causes

Most likely first.

1. Leak in brake hydraulic circuit B
2. Damaged brake line or hose
3. Leaking hydraulic component or connection

Symptoms

• Brake warning light
• Reduced braking performance or a change in brake-pedal feel
• Possible fluid loss

How to diagnose it

1. If the brake warning is on or the pedal feels abnormal, stop safely and do not continue driving; check the fluid reservoir only if it is safe to do so.
2. Inspect accessible circuit B brake lines and hoses for wetness, damage, or fluid trails, taking care not to confuse them with circuit A.
3. Check circuit B connections and hydraulic components for fresh fluid leakage.
4. Have the circuit B leak location confirmed and repaired, then inspect the rest of the hydraulic system for fluid loss.
5. After repair, verify fluid level, pedal feel, and system operation using the manufacturer’s procedure.

Common fixes

• Replace a leaking or damaged circuit B brake line or hose.
• Repair a leaking circuit B connection.
• Replace or repair the leaking hydraulic component in circuit B.
• Restore fluid level and bleed the brake system according to the manufacturer’s procedure.

Can I keep driving?

Do not drive with a suspected circuit B leak, reduced braking, or a changed pedal; braking can worsen suddenly. Arrange recovery and have the brakes repaired and checked before driving again.