Chassis, generic

C0540 Brake Pressure Sensor A Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

General electrical fault in the circuit of brake pressure sensor A, typically an interrupted signal, reference or ground wire, or a connection with excessive resistance. No manufacturer documents this exact code publicly; Mitsubishi, for example, maps its sensor-A faults to C0044 and C053D to C053F instead. The function is well described elsewhere: a Bosch patent has the master-cylinder pressure sensor report to the ESC controller, which lights ABS and ESC lamps and changes to a reduced or off state on a fault, and Saab 9-5 (2011) service data checks the 5-V feed and the signal wire for opens within 0.1 s and then shuts off ABS, traction and stability control until the next ignition cycle. Ordinary braking remains. Low and high voltages have their own codes, C053E and C053F.

Likely causes

Loose, corroded or pushed-out pin at the sensor or brake module connector
Broken signal, reference or ground wire
Internal open circuit in the pressure sensor

Symptoms

  • ABS and ESC warning lamps on
  • Stability and traction control out of service
  • Brake assist or hill-start assist missing

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,500
Time0.3–3 h

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

Parts involved

brake pressure sensor asensor wiring

Related codes

C053DC053EC053FC0544

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