Damaged or corroded wiring harness to the brake pressure sensor; Loose, dirty, or corroded electrical connector at the sensor; Failed brake pressure sensor; Blown fuse or faulty relay supplying power to the sensor circuit; High resistance or open circuit in the sensor supply wire; Faulty ABS control module (less common); Low brake fluid level or air in the hydraulic system affecting sensor readings

DTC codes / C05xx · Brakes, steering and suspension / C05C9

C05C9Brake Pressure Sensor Supply Circuit

Q: What does code C05C9 mean?

Brake Pressure Sensor Supply Circuit. C05C9 indicates that the antilock braking system (ABS) control module has detected an out-of-range voltage on the supply circuit feeding the brake pressure sensor, which is used to measure hydraulic pressure in the brake system. The module monitors the voltage on the sensor's power feed and sets this code when the signal falls outside the expected range, often due to a wiring fault, poor connection, or internal sensor failure.

C05C9 indicates that the antilock braking system (ABS) control module has detected an out-of-range voltage on the supply circuit feeding the brake pressure sensor, which is used to measure hydraulic pressure in the brake system. The module monitors the voltage on the sensor's power feed and sets this code when the signal falls outside the expected range, often due to a wiring fault, poor connection, or internal sensor failure.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

Illumination of the ABS warning light on the instrument cluster
Illumination of the traction control or stability control warning light, if equipped
A soft or spongy brake pedal feel in some cases
Reduced or disabled ABS function during hard braking
Often no symptoms besides the warning light, with normal brake performance
Intermittent warning light that may come and go with temperature or vibration

Common causes, most likely first

Damaged or corroded wiring harness to the brake pressure sensor
Loose, dirty, or corroded electrical connector at the sensor
Failed brake pressure sensor
Blown fuse or faulty relay supplying power to the sensor circuit
High resistance or open circuit in the sensor supply wire
Faulty ABS control module (less common)
Low brake fluid level or air in the hydraulic system affecting sensor readings

How to diagnose and fix it

Check the brake fluid level and inspect for leaks in the hydraulic system
Inspect the brake pressure sensor connector and wiring for damage, corrosion, or loose pins
Test the sensor supply circuit for proper voltage and ground using a digital multimeter
Check the fuse and relay that provide power to the brake pressure sensor circuit
Perform a resistance test on the sensor and compare to manufacturer specifications
Replace the brake pressure sensor if testing indicates it is faulty
Clear the code and verify the repair with a road test and scan tool

What the supply circuit code really means

A brake pressure sensor supply circuit code often results from a simple connector issue rather than a failed sensor, so always inspect the pins and terminals before replacing parts.
The sensor may share a power or ground circuit with other sensors, so a fault in a common wire can trigger multiple codes and mislead diagnosis.
In some vehicles, the ABS module sets this code when battery voltage is low or unstable, so check the charging system and battery condition first.
After replacing the sensor, the ABS module may require a calibration or relearn procedure, which is often overlooked and leads to a repeat code.
This code does not always mean the sensor is bad; a shorted or open wire in the harness can produce the same symptom, so circuit testing is essential.

Can I keep driving with C05C9?

The vehicle is generally safe to drive with this code because the base brakes remain functional, but ABS and stability control may be disabled. Avoid hard braking or slippery conditions until the fault is repaired, and have the system diagnosed promptly to restore full safety features.

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.