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DTC codes / C05xx · Brakes, steering and suspension / C05BE

C05BEBrake Booster Motor B Position Sensor Supply Circuit High

C05BE indicates that the antilock brake system (ABS) control module has detected an abnormally high voltage on the supply circuit feeding the brake booster motor's B position sensor. The module expects a stable reference voltage within a specific range, and a high reading tells it the sensor is receiving too much voltage, which can prevent accurate booster motor position feedback.

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

Symptoms you may notice

  • Illumination of the ABS warning light and possibly the traction control or stability control warning light
  • A hard brake pedal with increased effort required to stop the vehicle
  • Reduced or disabled power brake assist, especially at low speeds
  • The brake booster motor may run continuously or not at all
  • Often no symptoms besides the warning light, with normal brake feel in some vehicles
  • A stored diagnostic trouble code (DTC) in the ABS module with no other obvious drivability issues

Common causes, most likely first

  1. A short to voltage on the sensor supply circuit, often from chafed or pinched wiring
  2. A faulty brake booster motor B position sensor internally shorted to a higher voltage source
  3. Corrosion or water intrusion in the sensor connector or ABS module connector
  4. A defective ABS control module with an internal supply voltage regulator fault
  5. A poor ground connection for the sensor or booster motor, causing reference voltage to float high
  6. Aftermarket accessories or improper repairs that backfeed voltage into the sensor circuit

How to diagnose and fix it

  1. Connect a scan tool and record all ABS module codes and freeze-frame data to confirm C05BE is current and not history
  2. Visually inspect the brake booster motor B position sensor connector and wiring for corrosion, chafing, or loose pins
  3. Measure the sensor supply voltage at the sensor connector with the key on and compare to the manufacturer's specification
  4. Disconnect the sensor and recheck supply voltage to determine whether the high voltage originates in the wiring or the sensor
  5. Perform a wiggle test on the harness while monitoring supply voltage to expose intermittent shorts
  6. Check the ABS module ground and power feeds for voltage drops that could skew the reference supply
  7. If wiring and sensor test good, substitute a known-good sensor or module only after confirming all other circuits are intact

High supply voltage is not always the sensor

  • A shorted sensor is less common than a chafed supply wire rubbing against a 12-volt source, so inspect the harness routing near the booster motor before condemning parts.
  • The ABS module may set this code when its own internal 5-volt reference regulator fails, which means replacing the sensor will not fix the problem.
  • Water intrusion into the connector can create a conductive path that pulls the supply voltage high, especially after car washes or heavy rain.
  • A poor ground for the booster motor can cause the sensor supply to float high relative to the module's ground reference, mimicking a sensor fault.
  • Some scan tools show this code as pending or history after a low battery event, so clear it and verify it returns before starting diagnosis.

Can I keep driving with C05BE?

The vehicle remains drivable with reduced or absent power brake assist, but stopping distances increase and pedal effort is much higher, so avoid heavy traffic and high speeds until repaired. If the brake pedal feels normal and only the warning light is on, a cautious trip to a repair shop is acceptable, but do not tow heavy loads or drive in mountainous terrain.

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.

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