Chassis, generic

C05D4 Brake Master Cylinder Piston Position Sensor Calibration Not Learned

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

No valid zero calibration exists for the master cylinder piston travel sensors. GM's integrated controller stores the end-of-line zeroing of its pedal travel sensors in non-volatile memory and reloads it each drive; C05D4 sets within 10 ms after start if the stored status shows the learn failed. GM lists sensor electrical faults, a moving vehicle or applied brake during calibration, and an offset too large, too small or unsteady, plus memory errors (19OBDG03D and 25OBDG04B, Type A with MIL). Hitachi learns stroke sensor zeros only with no brake request and discards a run that is interrupted. After replacing the brake unit, perform the calibration with a scan tool on a stationary vehicle. C05CC/C05CF cover offsets learned but out of limit.

Likely causes

Zeroing not done after replacement of the brake unit
Calibration disturbed by vehicle movement or pedal input
Sensor offset too large, too small or unsteady
Memory error in the brake control module

Symptoms

  • Malfunction indicator lamp and brake warning after start
  • Brake system in reduced mode until calibrated

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–400
Time0.3–1.5 h

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

Parts involved

master cylinder pos sensorsbrake system control module

Related codes

C05CCC05CFC05C0C05C1

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