Chassis, generic

C0635 Brake Pressure Sensor G Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0635 flags a broken circuit at brake pressure sensor G: a supply, signal or ground wire without continuity, or a plug that has lost contact. No manufacturer publishes C0635 in this meaning, so it is unknown which part carries the letter G. A seventh sensor only exists in large units, for example the Lucas/ZF electro-hydraulic layout with four wheel sensors, one supply sensor and two front push-through sensors. What the module reads after an open depends on its input: per Honeywell, losing feed or ground sends the signal to the top rail if the input is pulled up, to the bottom if it is pulled down. Saab/GM books such an interruption after 0.1 s and switches off ABS and stability control. GM's PIP5094 lists C0635 from an older, unrelated GM numbering.

Likely causes

Plug at the sensor or hydraulic unit loose, corroded or with pushed-back terminals
Broken supply, signal or ground wire in the sensor harness
Internal interruption inside sensor G

Symptoms

  • ABS and ESC warning lamps on
  • Stability control and pressure-based brake functions switched off

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 gsensor wiring

Related codes

C0636C0637C0638C0639C05C8C05C9

References: patents.google.com, prod-edam.honeywell.com, saabwisonline.com, static.nhtsa.gov.