Chassis, generic

C0642 Brake Pressure Sensor K Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0642 means the output of sensor K exceeds its upper limit. Electro-hydraulic brakes like Mercedes' Sensotronic Brake Control work with a high-pressure accumulator and a pedal value sensor with two Hall elements; during a pre-drive check the unit pressurises the calipers to test, among other things, its pressure sensors. A high fault on any such sensor would make the module believe the brakes are applied. Saab's 9-5 sets its sensor code above 4.75 V for 0.1 s; GM's 2019 EBCM uses 95.24 % of supply on the main channel and 94.50 % on the reference channel. No maker says which sensor would be K, so the letter cannot be linked to a location. Typical: short to 5 V or battery, lost sensor ground, internal fault.

Likely causes

Signal shorted to 5 V or battery voltage
Lost sensor ground
Internal fault of sensor K signalled at the upper rail

Symptoms

  • Brake system and ESC warning lamps on
  • Brake lights or hold functions may be requested wrongly on some systems

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,600
Time0.5–3 h

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

Parts involved

brake pressure sensor ksensor wiring

Related codes

C0641C0643C0644C063EC0572

References: automotivetechinfo.com, gsi.ext.gm.com, saabwisonline.com.