Fault Family System: Chassis (C-Codes) 12 SAE Codes

Brake Master Cylinder Piston Position Sensor Circuit

Diagnostic & Technical Explanation

Code C05CA (Brake Master Cylinder Piston Position Sensor A Circuit Voltage High) sets when the brake-by-wire module cannot get a valid, correlated, or calibrated reading from the sensor tracking master cylinder piston travel, or the piston position or driver-applied pressure reads higher than the module expects for the given pedal input. On a decoupled brake-by-wire system this sensor is one of the module's primary inputs for building simulated pedal feel and confirming manual backup braking capability, so causes include a failed position sensor element, air or contamination affecting piston travel, or a cut-off valve that has not fully seated. Because master cylinder position feeds directly into the braking model, an uncalibrated or faulted sensor typically forces the system into a reduced-function backup mode.

These 12 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 12 times.

Codes in this family (12)

Code	Definition	Repair coverage
C05CA	Brake Master Cylinder Piston Position Sensor A Circuit Voltage High	4 ranked fixes
C05CB	Brake Master Cylinder Piston Position Sensor A Circuit Voltage Low	4 ranked fixes
C05CC	Brake Master Cylinder Piston Position Sensor A Circuit Range/Performance	4 ranked fixes
C05CD	Brake Master Cylinder Piston Position Sensor B Circuit Voltage High	4 ranked fixes
C05CE	Brake Master Cylinder Piston Position Sensor B Circuit Voltage Low	4 ranked fixes
C05CF	Brake Master Cylinder Piston Position Sensor B Circuit Range/Performance	4 ranked fixes
C05D0	Brake Master Cylinder Piston Position Sensor A/B Correlation	4 ranked fixes
C05D1	Brake Master Cylinder Piston Position Sensor Supply Circuit	4 ranked fixes
C05D2	Master Cylinder Piston Position Higher Than Expected	4 ranked fixes
C05D3	Driver Applied Pressure Higher Than Expected	4 ranked fixes
C05D4	Brake Master Cylinder Piston Position Sensor Calibration Not Learned	4 ranked fixes
C05D5	Brake Master Cylinder Cut Off Valve	4 ranked fixes

What this page does not show

This page publishes the fault mechanism and the code index. The licensed dataset adds, for every one of the 15,886 codes, the full authored repair set (56,729 procedures in total) with the fields deliberately withheld here:

Procedures 2..n after the first-listed procedure
Aftermarket parts cost ranges in USD (est_parts_cost_min/max_usd)
Professional labor-hour estimates (est_labor_hours)
Step-by-step diagnostic and repair instructions
Replacement-part mappings and catalog lookups
6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)

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