Chassis, generic

C05C9 Brake Pressure Sensor Supply Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Refers to the reference voltage the brake module provides to its hydraulic pressure sensors, not to one sensor's signal. If this feed collapses or rises, every sensor on it reads wrong at once, which is why the module checks the supply separately. Saab/GM monitors the 5 V reference of the brake pressure sensor and reacts within 0.1 s when that line touches ground or a voltage source. GM's integrated brake controller shows the usual window for such feeds: 4.85 to 5.15 V, held for 100 ms, on the pedal and motor sensor supplies (C05D1, C05BB). Tracking regulators like the TI TPS7B4253-Q1 are built for exactly this off-board sensor duty. No maker documents C05C9 itself. Unplug sensors one by one to find a shorted load.

Likely causes

Reference line shorted to ground or to battery voltage
One pressure sensor internally shorted, pulling down the shared feed
Sensor supply regulator inside the brake module defective

Symptoms

  • Several brake pressure codes at the same time
  • ABS, ESC and brake assist warnings, functions off

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,500
Time0.5–3 h

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

Parts involved

brake pressure sensor supplysensor supplybrake control module

Related codes

C05C6C05C7C05C8C05D1C056A

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