C0646Brake Pressure Sensor L Circuit High
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- C0646 means the signal of brake pressure sensor L lies above the band a real pressure can produce. A Kelsey-Hayes patent spells out the logic for a bridge-type brake sensor: a healthy output stays between zero and the supply voltage, so a reading equal to supply points to an open circuit, not to maximum pressure. A high code can therefore hide a lost ground or a broken signal line as well as a short to 5 V. Truck trailer brakes show where extra analog pressure sensors appear: WABCO's Trailer EBS D feeds an optional external brake pressure sensor from the modulator and reads it on a 0–5 V analog input. No carmaker documents C0646 or names its sensor L. Because a phantom pressure would suggest an application that is not taking place, the module stops trusting the channel.
- What you may notice
- ABS/ESC warning lamp on
- Stability control or electronic brake pressure control switched off
- Likely causes
- LikelySensor ground open, so the signal floats up to supply level
- PossibleSignal line shorted to the 5 V reference or battery voltage
- RareSensor electronics driving the output to its upper limit
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €1,600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.