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DTC codes / C05xx · Brakes, steering and suspension / C05A6

C05A6ABS Pump Motor Supply Voltage B Circuit High

C05A6 means the antilock braking system (ABS) control module has detected that the supply voltage on the pump motor's B circuit is higher than the expected range, typically near or above battery voltage when the pump should be off or at a controlled level. The module stores this code when the voltage on that dedicated feed circuit exceeds its calibrated threshold, indicating a short to voltage, a faulty pump motor, or a wiring problem rather than a normal low-voltage condition.

SystemChassis
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaBrakes, steering and suspension

Symptoms you may notice

  • The ABS warning light illuminates steadily on the dashboard, often accompanied by the traction control and stability control lights.
  • The ABS system may be disabled, so the wheels can lock during hard braking and the pedal may feel different or pulse abnormally.
  • Often no symptoms besides the warning light, especially if the overvoltage condition is intermittent or only occurs under specific electrical loads.
  • In some vehicles, the cruise control or hill-start assist may stop working because those functions rely on ABS wheel-speed data.
  • A faint electrical burning smell or a warm ABS pump motor area may be noticed if the pump motor is internally shorted and running when it should not be.
  • The battery may drain overnight or the ABS fuse may blow repeatedly if the high voltage is caused by a short to power on the pump circuit.

Common causes, most likely first

  1. A short to voltage on the pump motor B circuit wiring, often where the harness rubs against a metal bracket or passes near a high-current conductor.
  2. A faulty ABS pump motor with an internal short that backfeeds voltage onto the B circuit even when the module commands the motor off.
  3. A defective ABS control module with a failed internal driver or voltage-sensing circuit that incorrectly reports high voltage on the B circuit.
  4. Corroded or damaged connector pins at the ABS pump motor or control module that create a high-resistance path and voltage reflections.
  5. A poor ground connection for the ABS pump motor or module, which can cause the module to see an elevated voltage on the B circuit relative to its ground reference.
  6. An overcharging alternator or a battery with an intermittent high-voltage condition that raises the entire electrical system above normal, though this usually sets multiple codes.
  7. Aftermarket electrical accessories improperly tapped into the ABS pump circuit, injecting voltage when the pump should be isolated.

How to diagnose and fix it

  1. Verify the battery and charging system are healthy by checking battery voltage at rest and with the engine running, and load-test the battery if it is more than a few years old.
  2. Inspect the ABS pump motor harness and connector for chafed wires, corrosion, or loose pins, paying close attention to areas near sharp edges and heat sources.
  3. With the key on and the pump commanded off, measure voltage on the pump motor B circuit at the module connector and compare it to battery voltage to confirm the overvoltage condition.
  4. Disconnect the pump motor and recheck the B circuit voltage at the module; if the high voltage disappears, the pump motor is the likely source of the short.
  5. Check the ground circuit for the ABS pump motor and control module using a voltage drop test while cranking or operating the pump, repairing any high-resistance ground.
  6. If wiring and grounds are good, substitute a known-good ABS pump motor or control module as a test, following the manufacturer's diagnostic procedure for the specific vehicle.
  7. Clear the code and perform a road test with ABS activation to confirm the repair, then verify no related codes return after a full drive cycle.

What the B circuit voltage really tells you

  • A high voltage reading on the pump motor B circuit does not automatically mean the pump motor is bad; a shorted harness or a bad ground can make the module see high voltage on a circuit that is otherwise intact.
  • Many technicians replace the ABS pump motor only to find the code returns because the real problem is a corroded ground strap that raises the module's reference voltage and skews its voltage sensing.
  • This code can be set by a momentary voltage spike from a failing alternator or a jump-start, so always check for a stored history of overvoltage codes in other modules before condemning ABS parts.
  • The pump motor B circuit is often a dedicated feed that is only powered during ABS operation, so a short to voltage on that wire may not show up until the module runs a self-test or the pump is commanded on.
  • On some vehicles, the ABS module shares a ground with the body control module, and a poor body ground can cause this code along with unrelated electrical gremlins like flickering lights or false door-ajar warnings.

Can I keep driving with C05A6?

Because the ABS may be disabled and the pump motor circuit has a high-voltage fault that could overheat wiring or drain the battery, limit driving to a short distance to a repair shop and avoid heavy braking or slippery conditions. Do not continue driving if the warning light is accompanied by a burning smell or repeated fuse blowing.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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