Chassis, generic

C0647 Brake Pressure Sensor L Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Sensor L reads below its lowest valid value. In the Kelsey-Hayes scheme a near-zero bridge output is read as a probable short, because the sensor never reaches 0 V with a working circuit. Where the fault lies depends on the architecture: in a Continental Teves design the sensor in the hydraulic unit is only a bare Wheatstone bridge, and amplifier, offset correction and digitising sit in an IC on the control module, so a low reading can start on the board just as well as in the sensor. That patent also loads the factory calibration of each sensor, tied to its serial number, into the module. Typical causes: signal shorted to ground, collapsed sensor supply, damaged bridge. Which part a system calls L is not public; C0647 has no documented carmaker.

Likely causes

Signal path shorted to ground
Sensor supply missing or pulled down
Amplifier or input stage in the brake control module defective

Symptoms

  • ABS/ESC warning lamp on
  • Brake assist and stability control unavailable

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–1,800
Time0.5–4 h

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

Parts involved

brake pressure sensor lsensor wiring

Related codes

C0645C0646C0648C064BC064FC0643

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