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DTC codes / C06xx · Brakes, steering and suspension / C064A

C064ABrake Pressure Sensor M Circuit High

C064A is a generic chassis code indicating that the anti-lock brake system (ABS) control module has detected an abnormally high voltage on the electrical circuit for the 'M' brake pressure sensor. The module expects a voltage within a calibrated range that corresponds to hydraulic brake pressure, and a reading above the upper threshold triggers this code.

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

Symptoms you may notice

  • Illumination of the ABS warning light, and often the traction control and stability control lights as well.
  • A hard or unusually firm brake pedal feel if the sensor is used for brake assist or hill-hold functions.
  • Reduced or disabled ABS and traction control operation, which may be noticeable only during hard braking or slippery conditions.
  • Often no symptoms besides the warning light, with normal base braking performance.
  • In some vehicles, a message on the driver information center indicating a brake system fault or service required.
  • Unexpected activation or disabling of electronic parking brake or hill-start assist features that rely on brake pressure data.

Common causes, most likely first

  1. A short to voltage on the signal wire between the brake pressure sensor and the ABS module, often due to chafed insulation or a pinched harness.
  2. A faulty brake pressure sensor that internally shorts the signal circuit to a higher voltage reference.
  3. Corrosion or water intrusion at the sensor connector or ABS module connector, creating an unintended voltage path.
  4. A poor ground connection for the sensor or ABS module, causing reference voltage shifts that read as high signal voltage.
  5. An internal fault in the ABS control module that misinterprets or incorrectly biases the sensor signal circuit.
  6. Aftermarket electrical accessories or improper wiring repairs that backfeed voltage onto the sensor circuit.

How to diagnose and fix it

  1. Connect a scan tool and record all ABS and chassis codes, then clear codes and verify whether C064A returns immediately or after a road test.
  2. Visually inspect the brake pressure sensor, its connector, and the harness routing for damage, corrosion, or signs of fluid contamination.
  3. Measure reference voltage and signal voltage at the sensor connector with the key on and compare to the manufacturer's expected values.
  4. Disconnect the ABS module connector and check for voltage on the signal wire with the sensor disconnected to isolate a short to voltage.
  5. Perform a wiggle test on the harness while monitoring sensor voltage on the scan tool to catch intermittent shorts.
  6. If the circuit tests good, substitute a known-good sensor or perform a sensor sweep test to confirm the sensor is not internally shorted.
  7. If all external circuits and the sensor are verified good, diagnose or replace the ABS control module as the last step.

Why a brake pressure sensor reads high

  • A short to voltage on the signal wire is more common than a failed sensor, so technicians who replace the sensor first often see the code return.
  • The 'M' sensor designation varies by manufacturer; on some vehicles it is the master cylinder pressure sensor, while on others it is a secondary sensor in a stability control system, so always consult the service information for the exact location.
  • Water intrusion at the sensor connector can create a conductive path that mimics a short to voltage only when the vehicle is wet or after a car wash.
  • A failing ABS module ground can elevate the reference voltage for all pressure sensors, setting multiple pressure sensor codes at once rather than C064A alone.
  • Aftermarket alarm or remote start installations that tap into brake pedal wiring can backfeed voltage onto the sensor circuit and set this code without any factory component failure.

Can I keep driving with C064A?

The vehicle remains safe to drive under normal conditions because base hydraulic braking is unaffected, but ABS and stability control may be disabled. Avoid hard braking, slippery roads, and towing until the fault is repaired, and have the system diagnosed promptly.

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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