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DTC codes / C06xx · Brakes, steering and suspension / C064B

C064BBrake Pressure Sensor M Circuit Low

C064B means the antilock braking system (ABS) control module has detected an abnormally low voltage or current on the electrical circuit for the brake pressure sensor 'M', which is one of several pressure sensors used to monitor hydraulic brake pressure. The module compares the sensor signal against expected values and flags this code when the circuit stays below the low threshold for a calibrated time, indicating a short to ground, an open circuit, or a failed sensor.

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

Symptoms you may notice

  • ABS warning light illuminated on the dashboard, often accompanied by the traction control and stability control lights
  • A chime or message on the driver information display warning of a brake system fault
  • Reduced or disabled antilock braking function, though normal base braking usually remains
  • Traction control and electronic stability control systems may be deactivated as a consequence
  • Often no symptoms besides the warning light, with the vehicle driving and braking normally in dry conditions
  • In some cases, a soft or inconsistent brake pedal feel if the pressure sensor signal is used for pedal feel or hill-hold features

Common causes, most likely first

  1. Damaged, chafed, or corroded wiring in the brake pressure sensor 'M' circuit, especially near the sensor connector or where the harness flexes
  2. A failed brake pressure sensor 'M' itself, due to internal electrical failure or contamination
  3. Loose or corroded electrical connector at the sensor or at the ABS control module
  4. A short to ground in the signal or reference voltage wire for sensor 'M'
  5. An open circuit in the sensor ground or signal return path
  6. Low system voltage or a weak battery causing the ABS module to misread sensor inputs
  7. A fault within the ABS control module itself, though this is less common than wiring or sensor issues

How to diagnose and fix it

  1. Connect a scan tool and read all ABS and chassis codes to confirm C064B is current and not a stored history code from a previous event
  2. Visually inspect the brake pressure sensor 'M' connector and the harness for damage, corrosion, or loose pins, and check for any signs of brake fluid leakage
  3. Measure the sensor reference voltage and ground at the sensor connector with the key on, engine off, comparing against the manufacturer's specification
  4. Check the resistance of the sensor 'M' circuit between the sensor and the ABS module to detect opens or shorts, and wiggle-test the harness while monitoring the reading
  5. If wiring and connectors are good, substitute a known-good sensor 'M' or perform a resistance and voltage output test on the existing sensor to confirm failure
  6. Clear the codes and perform a road test to verify the repair, ensuring the ABS warning light stays off and no pending codes return
  7. If the fault persists after sensor and wiring checks, follow the manufacturer's diagnostic flow for the ABS module, including power and ground integrity and module replacement as a last resort

What most technicians miss on C064B

  • A low voltage code on a pressure sensor circuit is frequently caused by a poor ground connection rather than a failed sensor, so always load-test the ground circuit before condemning parts.
  • Brake pressure sensor 'M' is often one of several pressure sensors in the ABS hydraulic unit, and a single low circuit can be caused by a shared reference voltage wire that is shorted or open, affecting other sensors as well.
  • After replacing a brake pressure sensor, some vehicles require a calibration or learn procedure for the ABS module, and skipping it can leave the code stored or cause poor pedal feel.
  • A weak battery or charging system fault can set low-voltage codes across multiple modules, so check system voltage and battery health before chasing the sensor circuit.
  • The code can be set intermittently by vibration or temperature changes, so a wiggle test of the harness while watching live sensor data is more reliable than a static resistance check alone.

Can I keep driving with C064B?

The vehicle remains safe to drive in normal conditions because base braking is unaffected, but the ABS and stability control systems may be disabled, so avoid hard braking, slippery surfaces, and towing until the fault is repaired. If the brake pedal feels abnormal or the red brake warning light is also on, stop driving and have the vehicle inspected immediately.

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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