C05C3: Brake Booster Motor A Supply Circuit

What it means

The brake control module monitors the electrical supply circuit for brake booster motor A. It sets this code when the circuit voltage or current is outside the expected range.

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 booster motor A provides electric braking assist, and the brake control module monitors the motor's electrical supply. C05C3 is set when voltage or current in that supply circuit falls outside the expected range, which may result from a fuse, relay, wiring, connector, or motor fault.

Common causes

Most likely first.

1. Blown fuse or faulty relay
2. Open or damaged power wiring
3. Loose or corroded connector
4. Brake booster motor fault

Symptoms

• ABS warning light on
• ESC/stability control deactivated
• Possible reduced brake assist
• Speedometer may behave erratically

How to diagnose it

1. Scan the brake control module for related codes and freeze-frame data to see whether motor A's supply fault occurred during a braking event or at startup.
2. Check the relevant fuse and relay identified by the vehicle's wiring information for an open or poor connection.
3. Inspect motor A's power wiring and connector for damage, looseness, corrosion, or heat marks.
4. Measure supply voltage and check circuit continuity and current behavior using the manufacturer's procedure and specification.
5. If the supply wiring and relay are sound, assess motor A for an internal fault, then clear the code and verify operation.

Common fixes

• Replace a blown fuse after checking for the cause of the overload.
• Repair a loose, corroded, or damaged motor A power connection.
• Repair an open or damaged supply wire.
• Replace a faulty relay or motor A if testing confirms the component has failed.

Can I keep driving?

The electric booster may provide reduced or no assist, so avoid driving until pedal effort and braking are confirmed normal. If the pedal is hard or braking is impaired, stop safely and arrange recovery.