Open or damaged wire in the sensor B signal circuit; Short to voltage on the sensor B signal circuit; Faulty brake master cylinder piston position sensor B; Corroded or loose electrical connector at the sensor or ABS module; Failed ABS control module (internal circuit fault); Contaminated brake fluid or mechanical binding in the master cylinder affecting sensor reading

DTC codes / C05xx · Brakes, steering and suspension / C05CD

C05CDBrake Master Cylinder Piston Position Sensor B Circuit Voltage High

The C05CD code indicates that the anti-lock brake system (ABS) control module has detected an abnormally high voltage on the signal circuit for the brake master cylinder piston position sensor B. This sensor monitors the travel of the master cylinder piston, and a high voltage reading typically means the circuit is open, shorted to power, or the sensor itself has failed.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

Illumination of the ABS warning light and possibly the traction control and stability control lights
A stored code in the ABS module with no other drivability symptoms
Reduced or disabled ABS and traction control functions
A soft or spongy brake pedal feel in some cases
Intermittent warning light operation over bumps or when turning

Common causes, most likely first

Open or damaged wire in the sensor B signal circuit
Short to voltage on the sensor B signal circuit
Faulty brake master cylinder piston position sensor B
Corroded or loose electrical connector at the sensor or ABS module
Failed ABS control module (internal circuit fault)
Contaminated brake fluid or mechanical binding in the master cylinder affecting sensor reading

How to diagnose and fix it

Use a scan tool to verify the code and check for any related ABS codes or freeze-frame data
Inspect the sensor B connector and wiring for corrosion, chafing, or loose pins
Measure reference voltage and signal voltage at the sensor connector with the key on, engine off
Check the signal circuit for continuity to ground and for short to voltage using a multimeter
If wiring is good, test the sensor with a known-good unit or perform a resistance check if specified
Replace the faulty sensor or repair the wiring as needed, then clear codes and verify the repair
If the code persists after sensor and wiring checks, diagnose the ABS module for internal faults

What a high voltage code really means

A high voltage code on a sensor circuit almost always points to an open circuit or a short to power, not a failed sensor, so wiring inspection should come before part replacement.
The master cylinder piston position sensor is often integrated into the master cylinder assembly on many vehicles, making it a costly part to replace if misdiagnosed.
This code can be set by a low battery or charging system issue that causes the ABS module to see erratic voltages, so always check battery and charging system health first.
Some vehicles use the piston position sensor for hill-start assist and brake assist functions, so a fault may disable those features even if the brakes feel normal.
A code C05CD may appear after brake fluid replacement or master cylinder service if the sensor connector was disturbed or fluid contaminated the sensor.

Can I keep driving with C05CD?

You can usually drive the vehicle with this code, but the ABS and traction control systems may be disabled, which reduces safety in emergency braking or slippery conditions. Avoid hard braking and slippery roads until the fault is repaired.

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.