Faulty brake pressure sensor K; Damaged or corroded wiring or connector at the sensor; Contaminated or degraded brake fluid affecting pressure readings; Air trapped in the hydraulic system near the sensor; Failed ABS control module (internal fault in the sensor circuit); Mechanical issue with the brake master cylinder or hydraulic proportioning valve

DTC codes / C06xx · Brakes, steering and suspension / C0644

C0644Brake Pressure Sensor K Range/Performance

Q: What does code C0644 mean?

Brake Pressure Sensor K Range/Performance. C0644 indicates that the antilock braking system (ABS) control module has detected an out-of-range or erratic signal from the brake pressure sensor designated as 'K'. The computer expects a specific voltage or pressure reading within a calibrated window, and the sensor's output has fallen outside that window or is not behaving as expected during self-tests or normal braking.

C0644 indicates that the antilock braking system (ABS) control module has detected an out-of-range or erratic signal from the brake pressure sensor designated as 'K'. The computer expects a specific voltage or pressure reading within a calibrated window, and the sensor's output has fallen outside that window or is not behaving as expected during self-tests or normal braking.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

ABS warning light illuminated on the dashboard
Traction control or stability control warning light may also be on
Often no symptoms besides the warning light
Reduced or disabled ABS function during hard braking
Brake pedal may feel different or require more effort in some cases
Intermittent warning light that comes and goes with temperature or vibration

Common causes, most likely first

Faulty brake pressure sensor K
Damaged or corroded wiring or connector at the sensor
Contaminated or degraded brake fluid affecting pressure readings
Air trapped in the hydraulic system near the sensor
Failed ABS control module (internal fault in the sensor circuit)
Mechanical issue with the brake master cylinder or hydraulic proportioning valve

How to diagnose and fix it

Use a scan tool to read live data from brake pressure sensor K and compare to actual pedal pressure
Inspect the sensor connector and wiring for corrosion, chafing, or loose pins
Check brake fluid level and condition; bleed the brakes if air or contamination is suspected
Test the sensor's resistance and voltage output according to the manufacturer's procedure
Replace the brake pressure sensor K if it fails electrical or pressure-response tests
Clear the code and perform a road test to verify the repair
If the code persists, diagnose the ABS control module and its internal circuits

What most technicians overlook on C0644

A low brake fluid level or recent brake job that introduced air can set this code without any sensor fault.
Corroded pins in the sensor connector often mimic a failed sensor, so always inspect the harness before replacing parts.
Some vehicles use the brake pressure sensor for hill-start assist and stability control, so a fault can disable multiple systems.
The ABS module may store C0644 intermittently due to voltage drops from a weak battery or charging system.
After replacing the sensor, a calibration or learn procedure may be required on some models to clear the code permanently.

Can I keep driving with C0644?

The vehicle remains drivable in most cases, but ABS and stability control may be disabled, increasing stopping distances in emergency situations. Avoid hard braking and slippery conditions 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.