Chassis, generic

C05D1 Brake Master Cylinder Piston Position Sensor Supply Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Fault on the reference supply of the master cylinder piston (pedal travel) sensor. GM's integrated brake controller provides two 5 V supplies, each feeding one pedal travel channel and one motor position channel; C05D1 covers the first (PTS1/MPS1), C05BB the second. The supply fails below 4.85 V or above 5.15 V for 100 ms; for erratic dips a counter adds 50 per sample towards 800 (fastest 80 ms) and latches until key-off. All are Type A with MIL in 19OBDG03D and 25OBDG04B. Because the motor position channel shares the feed, motor sensor codes can appear at the same time. Tracking regulators such as the TI TPS7B4253-Q1 show how such off-board sensor supplies are built and protected.

Likely causes

Supply line shorted to ground or to another voltage
Pedal travel or motor position sensor loading the supply
Supply circuit on the control module board defective

Symptoms

  • Malfunction indicator lamp, brake warning and loss of assist
  • Further codes for pedal travel and motor position sensors

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,500
Time0.5–3 h

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

Parts involved

master cylinder pos sensor supplysensor supplybrake system control module

Related codes

C05CAC05CBC05BBC05D0

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