Code
C05CC
Generic
C — Chassis
Brake Master Cylinder Piston Position Sensor A Circuit Range/Performance
Views:
UK: 16
EN: 43
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or short in sensor wiring harness
- Corroded, loose, or contaminated connector at sensor or control module
- Failed or degraded piston position sensor
- Mechanical binding or sticking piston in master cylinder
- Contaminated brake fluid interfering with sensor or piston movement
- Faulty ABS/ESC control module or loss of reference voltage/ground
Symptoms
- ABS, ESC or brake warning lamp illuminated
- Brake pedal travel feels abnormal (longer or inconsistent)
- Intermittent loss of ABS/traction control functionality
- Stored or intermittent DTC related to brake sensors
- Possible changed brake pedal feel after stops/starts or during repeated braking
What to check
- Use a scan tool to read stored codes, freeze frame, and live data for piston position sensor A
- Visually inspect sensor connector and wiring for damage, corrosion, chafing or pinched sections
- Check brake fluid level and for signs of contamination or metal particles
- Wiggle the harness while watching live data to look for intermittent changes
- Confirm power (reference voltage) and ground at the sensor connector with key on
- Measure sensor signal while slowly depressing/releasing brake pedal or moving piston (observe smooth, monotonic change)
Signal parameters
- Typical (generic) analog sensor reference: ~5.0 V reference, signal output typically 0.1–4.9 V proportional to piston position (manufacturer-specific values vary)
- Expected behavior: smooth, monotonic change in voltage as piston moves with no sudden jumps or drops
- Resistance/continuity: wiring to module should show continuity; no short to battery (B+) or ground (0 V)
Diagnostic algorithm
- Retrieve and record C05CC and any related codes, freeze-frame, and live-data. Note conditions when fault set.
- Visually inspect master cylinder area, sensor connector, and wiring for damage, corrosion, contamination, or fluid leaks.
- With connector attached, back-probe reference/power and ground terminals. Verify reference voltage present (typically ~5 V) and good ground with key on (engine off).
- Monitor sensor signal while slowly applying and releasing brake pedal. Look for smooth voltage change; note out-of-range readings or step changes.
- If signal is out of range or absent, disconnect sensor and check wiring continuity back to ABS/ECU connector; check for short to ground or battery.
- Wiggle test harness and connectors while monitoring live data to find intermittent faults.
- If wiring and power/ground are good but signal remains faulty, remove and bench-test or replace the piston position sensor. Clean any contamination and inspect piston for binding or scoring; repair or replace master cylinder if mechanical fault found.
- If sensor and wiring test good, suspect ABS/ESC control module input fault—check module grounds and communications; consult manufacturer procedures.
- After repairs, clear codes and perform road or pedal-cycle test to confirm fault does not return.
Likely causes
- Damaged wiring harness or pinched cable near master cylinder
- Corroded connector causing intermittent contact
- Failed sensor due to internal damage or fluid ingress
- Piston mechanically binding due to contamination, seal failure, or debris
- Poor ground or missing reference voltage at sensor connector
Fault status
Status
Brake master cylinder piston position sensor A circuit range/performance fault — sensor output outside expected parameters or inconsistent during operation; stored when measured signal fails internal thresholds or plausibility checks.
Repair difficulty: Medium
Diagnostic time: 0.5-3.0 hours
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