Code C0646 indicates that the vehicle's control module has detected a higher than normal voltage in the left brake pressure sensor electrical circuit. This usually points to a short to power, a poor ground connection, or an internal failure within the sensor itself rather than actual excessive hydraulic pressure. It typically affects the anti-lock brakes (ABS) and stability control systems, which rely on accurate pressure readings to function properly.
The internal electronics of the sensor can short out, sending an abnormally high voltage signal back to the control module.
A chafed or damaged wire in the sensor circuit touching a power source will cause the signal voltage to spike abnormally.
A corroded or loose ground terminal for the sensor can cause the reference voltage to back-feed, resulting in a falsely high signal reading.
Water intrusion or bent pins in the sensor connector can alter the electrical resistance and cause a false high voltage condition.
Though rare, an internal fault in the control module could improperly pull up the sensor signal voltage or fail to read it accurately.
You can typically drive carefully, but your traction control and stability assist systems will likely be disabled, reducing vehicle safety in emergency maneuvers. Have it diagnosed soon.
No, the 'high' in this code refers to electrical voltage in the sensor circuit, not physical hydraulic pressure in the brake lines.
Rarely. Control modules are almost never the cause of a 'circuit high' code. Replacing the module without testing the sensor and wiring first is a common and costly mistake.
Yes. If the sensor lacks a proper ground path, the reference voltage can back-feed into the signal wire, causing the control module to see an abnormally high voltage.