Faulty brake pressure sensor A, causing erratic voltage output; Damaged or corroded wiring harness or connector at the sensor or ABS module; Poor electrical connection due to loose pins or water intrusion in the connector; Intermittent short or open circuit in the sensor signal or ground circuit; Contaminated or degraded brake fluid affecting sensor readings; Internal fault in the ABS control module interpreting sensor data incorrectly; Mechanical issue such as a sticking valve or air in the hydraulic system causing pressure fluctuations

DTC codes / C05xx · Brakes, steering and suspension / C056B

C056BBrake Pressure Sensor A Intermittent/Erratic

Q: What does code C056B mean?

Brake Pressure Sensor A Intermittent/Erratic. C056B indicates that the anti-lock brake system (ABS) module has detected an intermittent or erratic signal from brake pressure sensor A, which is typically the master cylinder pressure sensor. The computer sets this code when the sensor's voltage or pressure reading jumps, drops out, or behaves outside the expected range for a brief period, rather than failing completely.

C056B indicates that the anti-lock brake system (ABS) module has detected an intermittent or erratic signal from brake pressure sensor A, which is typically the master cylinder pressure sensor. The computer sets this code when the sensor's voltage or pressure reading jumps, drops out, or behaves outside the expected range for a brief period, rather than failing completely.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

ABS warning light illuminated on the dashboard, often intermittently
Traction control or stability control warning light may also be on
Brake pedal feels normal in most cases, but may occasionally feel soft or inconsistent
Momentary loss of ABS or traction control assistance during braking, especially in slippery conditions
Often no symptoms besides the warning light, with the code stored silently in the module
In rare cases, a slight pulsation or drag may be felt during light braking

Common causes, most likely first

Faulty brake pressure sensor A, causing erratic voltage output
Damaged or corroded wiring harness or connector at the sensor or ABS module
Poor electrical connection due to loose pins or water intrusion in the connector
Intermittent short or open circuit in the sensor signal or ground circuit
Contaminated or degraded brake fluid affecting sensor readings
Internal fault in the ABS control module interpreting sensor data incorrectly
Mechanical issue such as a sticking valve or air in the hydraulic system causing pressure fluctuations

How to diagnose and fix it

Inspect the brake pressure sensor and its connector for corrosion, damage, or loose pins, and clean or repair as needed
Check the sensor wiring harness for chafing, breaks, or shorts, and perform a wiggle test while monitoring live data
Verify brake fluid level and condition, and bleed the brake system if contamination or air is suspected
Use a scan tool to monitor brake pressure sensor A live data for erratic or inconsistent readings while pressing the brake pedal
Perform a voltage drop test on the sensor signal and ground circuits to identify high resistance or intermittent faults
If the sensor signal is erratic and wiring is good, replace the brake pressure sensor A and clear the code
If the code persists after sensor replacement, diagnose the ABS module for internal faults or reprogramming needs

Intermittent brake pressure sensor faults

A common misdiagnosis is replacing the ABS module when the actual problem is a chafed wire near the master cylinder that only shorts when the engine moves under load.
Brake pressure sensor A is often the master cylinder pressure sensor, but on some vehicles it may be a wheel cylinder pressure sensor; always confirm the location in the service information before testing.
Intermittent codes like C056B can be set by a low battery or charging system issue that causes voltage spikes, so check battery health and grounds before condemning the sensor.
The code may appear only during cold starts or after the vehicle sits, when moisture in a connector causes a temporary short that clears as the engine warms.
A sticking brake caliper or restricted brake hose can cause pressure fluctuations that mimic a sensor fault, so inspect the entire hydraulic system for mechanical issues.

Can I keep driving with C056B?

You can generally continue driving with C056B, but be aware that ABS and traction control may be disabled, reducing safety in emergency braking or slippery conditions. Avoid heavy braking and wet or icy roads until the fault is repaired, and have the system diagnosed promptly.

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.