Home›Trouble Codes›C0644

C0644 — Brake Pressure Sensor K Rangeperformance

Generic OBD-II · all makesChassis

OBD-II code C0644 indicates the brake pressure sensor 'K' signal is outside the expected range or performance specifications. This typically means the sensor's output voltage or signal does not match the expected values during brake system operation, potentially affecting vehicle stability or braking performance.

Symptoms

What causes it — most likely first

1. Faulty brake pressure sensor 'K'

The sensor itself may be damaged, contaminated, or internally failed, causing it to send incorrect voltage signals to the control module.

2. Wiring or connector issues

Corrosion, fraying, or loose connections in the wiring harness or connector between the sensor and the control module can disrupt signal transmission.

3. Brake fluid contamination or incorrect level

Contaminated or improperly filled brake fluid can affect sensor readings, as the sensor relies on hydraulic pressure changes to function correctly.

4. Mechanical brake system issues

Problems such as a stuck brake caliper, collapsed brake hose, or master cylinder failure can cause abnormal pressure readings.

5. ABS or stability control module software glitch

A temporary software error in the control module may misinterpret sensor data, though this is less common than hardware or wiring issues.

6. Control module (ABS/ECM/PCM) failure

While rare, a malfunctioning control module could incorrectly flag the sensor signal as out of range. This is typically a last-resort diagnosis after other causes are ruled out.

How it's diagnosed

  1. Retrieve and document all stored trouble codes, including freeze frame data, to understand the conditions under which the code was set.
  2. Visually inspect the brake pressure sensor 'K' and its wiring harness for damage, corrosion, or loose connections. Check for signs of fluid leaks near the sensor.
  3. Measure the sensor's voltage output using a multimeter or oscilloscope, comparing readings to manufacturer specifications during key-on and brake application.
  4. Test the brake fluid for contamination and verify the fluid level is within the specified range. Inspect the brake system for mechanical issues (e.g., caliper function, hose condition).
  5. Check for technical service bulletins (TSBs) related to the brake pressure sensor or control module software updates that may address known issues.
  6. If all other components test normally, consider testing or replacing the control module, though this is rarely the root cause for C0644.

Code facts & related codes

SystemChassis
StandardizationSAE generic — identical on every make
Related codesC0640 — Brake Pressure Sensor J RangeperformanC0641 — Brake Pressure Sensor K CircuitopenC0642 — Brake Pressure Sensor K Circuit HighC0643 — Brake Pressure Sensor K Circuit LowC0645 — Brake Pressure Sensor L CircuitopenC0646 — Brake Pressure Sensor L Circuit High

Frequently asked

Is the brake pressure sensor the only part that can cause C0644?

No. While a faulty sensor is the most common cause, wiring issues, brake fluid problems, or mechanical brake system failures can also trigger this code. Always inspect the entire system before replacing parts.

Will replacing the ABS control module fix C0644?

Replacing the control module is rarely necessary for this code. The module is often blamed incorrectly when the issue lies with the sensor, wiring, or brake system. Only consider module replacement after all other potential causes have been ruled out.

Can I drive with C0644 stored in the system?

Driving with this code active may result in reduced brake performance or disabled stability control systems, which can compromise vehicle safety. It is recommended to diagnose and repair the issue as soon as possible.

Why does the code mention 'range/performance' instead of a simple failure?

The 'range/performance' designation means the sensor is providing a signal, but the values are outside expected parameters (e.g., too high, too low, or erratic). This differs from a complete signal loss, which would trigger a different code.