C05C9: Brake Pressure Sensor Supply Circuit

What it means

The brake control module monitors the supply voltage used by the brake pressure sensors. It sets this code when the shared supply circuit is outside its expected electrical 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

The brake control module supplies power to the brake pressure sensors through a shared supply circuit. This code sets when that supply is outside its expected electrical range, potentially affecting several pressure readings and related ABS or stability functions.

Common causes

Most likely first.

1. Open or short in the sensor supply wiring
2. Blown fuse or faulty supply from the control module
3. Loose or corroded connector
4. A pressure sensor internally shorted and pulling down the supply

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 module for other pressure-sensor codes and review freeze-frame and live data to see whether multiple sensor readings failed together.
2. Inspect the shared supply wiring, connectors, and relevant fuse for looseness, corrosion, water ingress, or visible damage.
3. Check the supply circuit and ground connections using the vehicle wiring information and compare measurements with the manufacturer's specification.
4. If the supply is being pulled down, isolate the pressure sensors one at a time as directed by the manufacturer to identify a sensor that is internally shorted.
5. If the wiring, fuse, and sensors check out, test the brake module's supply output according to the manufacturer's procedure.

Common fixes

• Clean and secure a loose or corroded shared supply connector.
• Replace a blown fuse after checking for the cause of the overload.
• Repair an open or shorted section of the shared sensor supply wiring.
• Replace a pressure sensor that tests as internally shorted.
• Repair or replace the brake module only if its supply output fails the manufacturer's test.

Can I keep driving?

ABS or stability control may be disabled, and brake assist may be reduced. Avoid high speeds and hard braking, and stop safely if braking feels abnormal or reduced.