C05A7: ABS Pump Motor Supply Voltage B Circuit Low

What it means

ABS pump motor supply B below expected range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

At a glance

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

How it works

Supply voltage B powers the ABS pump motor, which the brake control module operates to regulate hydraulic pressure during ABS braking. C05A7 sets when supply B voltage is below its expected range, often because of a weak supply, excessive resistance, or damaged wiring.

Common causes

Most likely first.

1. Weak supply or high resistance
2. Connector pins corroded - high contact resistance
3. Harness chafing through insulation

Symptoms

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

How to diagnose it

1. Read ABS codes and freeze-frame data to confirm the low supply B condition and check for related battery, charging, fuse, or pump faults.
2. Inspect the ABS pump motor supply B connector and harness for corrosion, loose or pushed-back terminals, and chafing.
3. Check the supply fuse and power and ground connections shown in the wiring diagram for looseness or damage.
4. Measure supply B voltage under the conditions specified by the manufacturer and compare it with the manufacturer's specification, checking for voltage drop across connections.
5. If the external supply circuit passes, test the pump motor load and brake module output using the manufacturer's procedure.

Common fixes

• Clean and secure a loose or corroded supply B connection.
• Repair chafed wiring or replace a damaged connector terminal.
• Restore a weak power or ground connection and replace a failed fuse after finding its cause.
• Repair or replace the pump motor or brake module only if testing identifies an internal fault.

Can I keep driving?

ABS and stability control may be unavailable if the pump cannot receive enough power, while normal braking may remain. Drive cautiously, allow extra stopping distance, avoid slippery conditions, and stop if braking performance changes.