Chassis, generic

C0639 Brake Pressure Sensor H Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Sensor plug loose or terminals corroded
Supply, signal or ground conductor broken
Open measuring bridge or failed electronics inside the sensor

Symptoms

  • ABS and ESC lamps on, possibly flickering with vibration
  • ABS or stability control disabled

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–1,500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake pressure sensor hsensor wiring

Related codes

C063AC063BC063CC0635C063D

References: patents.google.com, patents.google.com, patents.google.com.