A weak or failing vehicle battery that cannot maintain adequate voltage under load, especially during ABS pump activation.; Corroded, loose, or damaged wiring and connectors in the ABS pump motor supply circuit, including the ground circuit.; A blown high-current fuse or a faulty relay that supplies power to the ABS pump motor.; High resistance in the power supply circuit due to a partially broken wire or poor splice, often caused by corrosion or rodent damage.; A failing ABS pump motor that draws excessive current, causing a voltage drop that the module interprets as a low supply voltage.; A faulty ABS control module with an internal voltage monitoring circuit error, though this is less common than external circuit issues.

DTC codes / C05xx · Brakes, steering and suspension / C055B

C055BABS Pump Motor Supply Voltage Circuit A Low

Q: What does code C055B mean?

ABS Pump Motor Supply Voltage Circuit A Low. C055B indicates that the anti-lock brake system (ABS) control module has detected an abnormally low voltage on the power supply circuit that feeds the ABS pump motor, specifically on circuit A. The module monitors the voltage at the pump motor supply terminal and sets this code when the voltage falls below a calibrated threshold, which can prevent the pump from running during an ABS event.

C055B indicates that the anti-lock brake system (ABS) control module has detected an abnormally low voltage on the power supply circuit that feeds the ABS pump motor, specifically on circuit A. The module monitors the voltage at the pump motor supply terminal and sets this code when the voltage falls below a calibrated threshold, which can prevent the pump from running during an ABS event.

SystemChassis

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

The ABS warning light is illuminated on the dashboard, often with no other symptoms noticed by the driver.
The traction control system (TCS) may also be disabled, triggering a separate warning light if equipped.
During hard braking or slippery conditions, the ABS may not activate, leading to wheel lockup and reduced steering control.
The brake pedal may feel unusually firm or unresponsive during emergency braking because the pump cannot build pressure.
In some vehicles, a chime or message such as 'Service ABS' may appear in the driver information center.

Common causes, most likely first

A weak or failing vehicle battery that cannot maintain adequate voltage under load, especially during ABS pump activation.
Corroded, loose, or damaged wiring and connectors in the ABS pump motor supply circuit, including the ground circuit.
A blown high-current fuse or a faulty relay that supplies power to the ABS pump motor.
High resistance in the power supply circuit due to a partially broken wire or poor splice, often caused by corrosion or rodent damage.
A failing ABS pump motor that draws excessive current, causing a voltage drop that the module interprets as a low supply voltage.
A faulty ABS control module with an internal voltage monitoring circuit error, though this is less common than external circuit issues.

How to diagnose and fix it

Perform a battery and charging system test to confirm the battery holds a stable voltage under load and the alternator is charging correctly.
Inspect the ABS pump motor supply circuit wiring and connectors for corrosion, looseness, or damage, and repair as needed.
Check the high-current fuse and relay that feed the ABS pump motor, replacing any that are blown or faulty.
Measure voltage at the ABS pump motor supply terminal while the pump is commanded on with a scan tool, looking for excessive voltage drop.
Perform a voltage drop test on both the power and ground sides of the pump motor circuit to locate high-resistance points.
If the circuit and power supply are good, test the ABS pump motor directly by applying power and ground to confirm it operates without excessive current draw.
Replace the ABS control module only after all external circuit and component tests have passed, as it is the least likely cause.

Why a low ABS pump voltage is often a wiring issue

A common oversight is assuming the ABS module is at fault when the real problem is a weak battery or a corroded ground connection that only shows up under the high current demand of the pump motor.
The code can be set intermittently by a failing relay that works fine during static testing but drops voltage when the pump is commanded on, so a relay swap with a known-good unit is a quick diagnostic step.
Voltage drop testing under load is far more reliable than simply checking for continuity, because a single strand of wire can pass a continuity test but fail under the pump's current draw.
Some vehicles share the ABS pump motor supply circuit with other high-current systems, so a fault in a related circuit can cause this code without any issue in the ABS wiring itself.
A scan tool that can command the ABS pump motor on is essential for reproducing the fault, as the code may not set during normal driving if the pump is rarely activated.

Can I keep driving with C055B?

Because this fault can disable the anti-lock braking system and traction control, the vehicle may be unsafe in emergency braking or slippery conditions. Drive cautiously, avoid hard braking and slippery roads, and have the vehicle inspected by a qualified technician as soon as possible.

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.