Chassis, generic

C05D0 Brake Master Cylinder Piston Position Sensor A/B Correlation

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Both travel channels are individually plausible, but they disagree with each other. GM's integrated controller votes two out of three: PTS1, PTS2 and a third travel estimate (BAS); if PTS1 and PTS2 differ by more than 2 mm and one of them also deviates from the third value by over 2 mm, that channel is declared failed after 100 ms. The XT4 booster module allows 2.71 mm, the 23OBDG07 and 25OBDG03B tables 1.5 mm, each for 0.12 s with both channels initialised and otherwise fault-free; all Type A with MIL. Continental describes pedal modules with two travel sensors precisely so a single bad one can be identified. Loose sensor mounting, contamination and connector faults on one channel are typical causes. C05CC/C05CF cover each channel alone.

Likely causes

One sensor channel drifting away from the other
Mechanical play at the sensor or input rod
Contact resistance on one channel only

Symptoms

  • Malfunction indicator lamp and brake warning
  • Brake system switches to reduced mode, regeneration may be off

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 amaster cylinder pos sensor b

Related codes

C05CCC05CFC05D1

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