Code C0649 indicates that the vehicle's control module has detected an open circuit in the brake pressure sensor 'M' signal circuit. The control module expects a voltage signal from this sensor that correlates with applied brake hydraulic pressure, and an open means that signal path is broken or out of expected range. This typically affects electronic brake, stability, or regenerative-braking systems that rely on accurate brake-pressure input.
Corroded, broken, or backed-out terminals at the brake pressure sensor connector are the most common cause of an open-circuit fault.
The sensor's internal element or signal circuit can fail open, producing no return voltage to the control module.
Chafed, rodent-damaged, or heat-damaged harness wiring between the sensor and the control module can interrupt the signal path.
A lost reference voltage or ground feed to the sensor will appear to the module as an open signal circuit.
Rare; an internal open in the module's sensor input circuit is possible only after wiring, sensor, and power/ground checks are cleared.
Basic hydraulic braking usually still functions, but ABS, stability control, or regenerative braking may be disabled. Have it diagnosed promptly, especially in a hybrid or EV.
Not necessarily. An open circuit is more often caused by wiring, connector, or terminal issues than by the sensor itself. Proper circuit testing is required before replacing the sensor.
Usually no. Control-module failure is rare for this code and is frequently misdiagnosed. Wiring, connector, and sensor faults should be ruled out first; a module should only be considered after all external checks pass.
A weak power or ground supply to the sensor can mimic an open circuit, so verifying stable reference voltage and ground is part of correct diagnosis.