Damaged or corroded wiring or connector at the ABS pump motor or control module; Blown fuse or failed relay in the ABS pump motor supply circuit; Open circuit in the power or ground wire to the pump motor (broken wire, loose terminal); Failed ABS pump motor (internal open circuit or worn brushes); Faulty ABS control module (internal driver or voltage sensing circuit); High resistance or corrosion at the battery or ground connections affecting supply voltage; Aftermarket accessories or poor previous repairs tapping into the circuit

DTC codes / C05xx · Brakes, steering and suspension / C05A5

C05A5ABS Pump Motor Supply Voltage B Circuit/Open

Q: What does code C05A5 mean?

ABS Pump Motor Supply Voltage B Circuit/Open. The anti-lock braking system (ABS) control module has detected an open circuit or abnormal voltage on the supply circuit for the ABS pump motor, specifically the 'B' side or secondary supply line. This means the module cannot reliably power the pump motor that builds hydraulic pressure during ABS activation, so it disables ABS function and turns on the warning light.

The anti-lock braking system (ABS) control module has detected an open circuit or abnormal voltage on the supply circuit for the ABS pump motor, specifically the 'B' side or secondary supply line. This means the module cannot reliably power the pump motor that builds hydraulic pressure during ABS activation, so it disables ABS function and turns on the warning light.

SystemChassis

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaBrakes, steering and suspension

Symptoms you may notice

ABS warning light illuminated on the dashboard
Traction control and stability control lights may also be on if those systems share the pump
Often no symptoms besides the warning light during normal driving
ABS may not activate during hard braking or slippery conditions, increasing stopping distance
Pump motor may not run during a self-test, which a technician can hear or feel
In some vehicles, a chime or message indicating a brake system fault

Common causes, most likely first

Damaged or corroded wiring or connector at the ABS pump motor or control module
Blown fuse or failed relay in the ABS pump motor supply circuit
Open circuit in the power or ground wire to the pump motor (broken wire, loose terminal)
Failed ABS pump motor (internal open circuit or worn brushes)
Faulty ABS control module (internal driver or voltage sensing circuit)
High resistance or corrosion at the battery or ground connections affecting supply voltage
Aftermarket accessories or poor previous repairs tapping into the circuit

How to diagnose and fix it

Check the ABS fuses and relays related to the pump motor supply and replace any that are blown or faulty
Inspect the wiring harness and connectors at the ABS pump motor and control module for corrosion, damage, or loose pins
Measure battery voltage and ground integrity at the ABS module and pump motor connector with a multimeter
Perform a voltage drop test on the supply and ground circuits while the pump motor is commanded on with a scan tool
Command the ABS pump motor on with a bidirectional scan tool and listen for operation; if it does not run, test the motor directly
If the motor does not run with direct power and ground, replace the ABS pump motor or assembly as required
If all circuits and the motor test good, diagnose or replace the ABS control module

What the ABS pump supply code really means

A weak or failing battery can cause this code because the ABS module monitors supply voltage and may set a fault if voltage drops during pump motor activation.
Corroded ground connections, especially at the chassis or engine block, are a frequent hidden cause of supply voltage faults on ABS circuits.
The code can be set intermittently by a loose connector that only loses contact during vibration or temperature changes, so a wiggle test while monitoring live data is valuable.
Some vehicles use a shared power supply for the ABS pump and other high-current systems, so a fault in an unrelated circuit can affect the ABS supply.
Replacing the ABS pump motor without checking the relay and wiring first is a common misdiagnosis that leads to repeat failures.

Can I keep driving with C05A5?

The vehicle remains driveable with normal braking, but ABS is disabled, so avoid hard braking or slippery conditions where ABS would be needed. Have the fault diagnosed promptly, especially if the brake warning light is also on.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.