Chassis, generic

C05CC Brake Master Cylinder Piston Position Sensor A Circuit Range/Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Channel A (GM calls it PTS1) delivers a travel value that is electrically valid but physically wrong. GM's integrated controller with pedal simulator, the vacuum-free design ZF supplies, checks three things: travel above 38 mm (normal input piston travel is about 25 mm, about 36 mm without boost), a change faster than 700 mm/s, and a learned offset beyond 2.5 mm, each 100 ms, Type A. In the XT4 booster module the zero offset with pedal released may not exceed 0.9 mm while driving and accelerating; 23OBDG07 and 25OBDG03B allow +1.1/-1.5 mm. Causes range from a failed sensor to a bent sensor rod or wrong mounting. C05CF is the same check on channel B, C05D0 compares both channels.

Likely causes

Sensor A offset drifted beyond the learn limit
Damaged travel sensor rod or mounting
Intermittent signal line producing jumps
Pedal not fully returning (floor mat, return spring)

Symptoms

  • Malfunction indicator lamp and brake warning
  • Changed pedal feel or reduced assist
  • Brake lights may react inconsistently

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 aelectric brake booster

Related codes

C05CAC05CBC05CFC05D0

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