C0639Brake Pressure Sensor H Circuit/Open
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- Brake pressure sensor H has lost its electrical connection: an interrupted 5 V feed, signal or ground line, or a loose plug at the hydraulic unit. No published service data ties C0639 to a real part. Layouts with eight sensors do exist: a Toyota patent places pressure sensors at the pump and accumulator output, ahead of the pressure-increasing valve, in the master cylinder and booster chambers and at all four wheel cylinders. With a pull-down input, Denso shows that a cut supply or signal line ends at 0 V while a cut ground climbs above 4.7 V, so an open may surface as C063B or C063A instead. Kelsey-Hayes plugs its sensor straight into the module board to avoid a harness and watches for an open or shorted bridge; on a failure ABS is disabled and a lamp lit.
- What you may notice
- ABS and ESC lamps on, possibly flickering with vibration
- ABS or stability control disabled
- Likely causes
- LikelySensor plug loose or terminals corroded
- PossibleSupply, signal or ground conductor broken
- RareOpen measuring bridge or failed electronics inside the sensor
- Repair
- Medium · Usually a job for a workshop.Typical cost: €40 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.