C0566: Brake Booster Solenoid Circuit/Open

What it means

The brake booster solenoid circuit is open or lacks electrical continuity. The brake booster system may not operate as intended.

At a glance

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

How it works

The brake booster solenoid is an electrically controlled part of the brake-assist system. This code sets when its circuit has an open path or lacks continuity, so the solenoid may not respond as intended.

Common causes

Most likely first.

1. Wiring break or coil open
2. Pin pushed back out of connector body
3. Cracked solder joint inside the module or sensor

Symptoms

• Brake or ABS warning light
• Brake assist may be reduced, depending on the system

How to diagnose it

1. Read brake-module freeze-frame and live data for the solenoid command and any related brake-assist codes.
2. Inspect the booster solenoid connector for a disconnected plug, pushed-back pin, corrosion, or damaged terminals.
3. Trace the solenoid wiring for a break, chafing, or damage near the booster and module.
4. With the correct wiring diagram, check continuity through the solenoid and its control circuit, including connector terminals.
5. If the harness and solenoid pass, test the controlling module circuit using the manufacturer's procedure before condemning the module.

Common fixes

• Reconnect and secure the brake booster solenoid connector.
• Repair a broken wire or loose terminal in the solenoid circuit.
• Replace the solenoid if its coil is confirmed open.
• Repair the control module only if circuit testing confirms an internal fault.

Can I keep driving?

Brake assist may be reduced, so pedal effort or stopping distance could increase. Avoid unnecessary driving; if the pedal feels unusually hard or braking is impaired, stop safely and have the vehicle inspected before driving further.