AU
C05CD00

DTC C05CD00 indicates the signal voltage of master cylinder piston position sensor B inside the IPB (Intelligent Integrated Braking System) continuously exceeds the calibrated threshold (typically >4 — Atto 3

Braking System

DTC C05CD00 indicates the signal voltage of master cylinder piston position sensor B inside the IPB (Intelligent Integrated Braking System) continuously exceeds the calibrated threshold (typically >4.8V).

This Hall-effect position sensor monitors the brake master cylinder piston travel position in real time.

It provides the IPB with an accurate brake pedal input signal to enable brake-by-wire assist, coordinated energy recovery, and ESC intervention.

This high voltage indicates a short to power in the sensor signal circuit, an internal sensor breakdown short, or an IPB control module sampling circuit fault.

This fault forces the IPB into degraded mode, which causes abnormal brake assist (stiff pedal or altered pedal travel), disables the energy recovery system, and limits ESP/ABS functions.

In extreme cases, it compromises braking performance.

This is a safety-related fault.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Damaged master cylinder position sensor B inside the IPB electro-hydraulic module: The sensor is highly integrated with the IPB. A fault in the internal Hall element or signal processing circuit causes abnormally high output voltage. This is the most common root cause.
  • 2Wiring harness short circuit: The sensor signal wire (usually the standard 5V reference voltage circuit) shorts to the vehicle 12V power wire or 5V reference voltage line, pulling the voltage high.
  • 3Connector issue: Water ingress, corrosion, or bent pins in the IPB module connector cause abnormal continuity between the signal and power terminals. This commonly occurs after wading or high-pressure washing.
  • 4IPB power supply fault: The 12V supply voltage to the IPB module increases abnormally (e.g., alternator regulator fault), shifting the internal sensor supply reference.
  • 5Software calibration error: In rare cases, the IPB control software contains an incorrect Sensor B voltage threshold calibration or loses calibration data, triggering a false fault (reflash the software to resolve).
What To Do
  • 1
    Safety Confirmation and Preliminary Inspection: Confirm the brake fluid level is normal. Inspect the IPB module for physical damage and brake fluid leaks. Check the instrument panel warning light status (ABS/ESP/brake system lights). Read all fault codes and record freeze frame data using the VDS2000/VDS6000 diagnostic tool. Confirm DTC C05CD00 is a current fault, not a history fault.
  • 2
    Data stream analysis: Access the IPB system to read the real-time voltage data of Master Cylinder Position Sensor B. Check if the voltage remains above 4.8V (normal range is typically 0.5-4.5V). Simultaneously check the Sensor A voltage for comparison. If Sensor A is normal and Sensor B is abnormal, initially rule out a shared power supply issue.
  • 3
    Wiring harness and connector inspection: Disconnect the IPB module low-voltage connector (usually located near the firewall). Verify the connector seal is intact and inspect the pins for water corrosion (blue-green oxide) or burn marks. Use a multimeter to measure the Sensor B signal wire resistance to ground (should be infinite) and continuity to the 12V power supply (should show no continuity). Inspect the wiring harness for abrasion or damaged insulation causing contact with the vehicle power wire.
  • 4
    Sensor and module inspection: Measure the 5V reference voltage for Sensor B at the IPB connector (normal: 4.9-5.1V). If the supply is normal but the internal output is abnormal, diagnose an internal IPB fault. If the supply voltage is too high, check the vehicle power supply system. Measure the resistance between the Sensor B signal wire and ground to confirm there is no short circuit.
  • 5
    IPB assembly replacement: Master cylinder position sensor B is integrated into the IPB and is not serviceable separately. Replace the complete IPB electro-hydraulic module assembly. Before replacement, power down the old module, disconnect the battery negative terminal, and protect the brake lines to prevent brake fluid loss.
  • 6
    System matching and calibration: After installing the new IPB, connect the diagnostic tool and perform: ① Brake system bleeding procedure (perform electronic bleeding in the sequence: front left - front right - rear left - rear right); ② Master cylinder position sensor calibration (sensor zero-position learning); ③ Brake pedal position learning; ④ Clear all fault codes and perform a road test to confirm normal brake assist operation and that the fault code does not recur.
Real-World Cases
BYD DTC AI Analysis

BYD Seal IPB master cylinder sensor B circuit fault

✓
2022 Seal 700km Long Range variant, 23,000 km. Owner reported intermittent "Check Braking System" message on the instrument cluster, ESP warning light on, and occasional hard brake pedal. VDS scan retrieved IPB code C05CD00 (current fault); master cylinder position sensor B voltage read 5.12V (exceeding 4.8V upper limit). IPB module had no external damage and the connector showed no water ingress. Measured sensor B signal line: intermittent short to 5V reference. Replaced IPB assembly, performed sensor calibration and brake bleeding. Fault resolved. Root cause: cold solder joint on the sensor signal trace inside the IPB PCB caused intermittent short to 5V reference.
Original source ↗
BYD DTC AI Analysis

Song PLUS DM-i brake booster abnormality, DTC C05CD00

✓
2021 Song PLUS DM-i, 18,000 km. Owner reported sudden increased brake pedal travel at high speed, requiring heavy pedal pressure to brake, with multiple brake warning lights on. Towed to the shop, VDS scan of the IPB system showed DTCs C05CD00 and C05CF00 (Sensor B Performance Range). Live data showed Sensor B voltage fixed at 5.0 V, not changing with pedal movement. Inspection of the IPB connector found pin 12 (signal wire) slightly backed out and contacting adjacent pin 14 (12 V supply), pulling the signal voltage high. Repaired the pin and resecured the connector. Voltage returned to normal. Cleared the DTCs and road-tested 20 km with no fault recurrence.
Original source ↗
BYD DTC AI Analysis

Pre-delivery IPB sensor fault on new Dolphin

✓
2023 Dolphin Fashion Edition. During PDI, the instrument cluster displayed 'Brake System Fault' and the vehicle could not be delivered. Scanner read DTC C05CD00 (Master Cylinder Position Sensor B Voltage Too High). Brand new vehicle with only 15 km. Visual inspection of the IPB module and wiring harness showed no abnormalities or water ingress. IPB supply voltage measured 12.4V (normal), but Sensor B output was 5.3V. Performed IPB software upgrade (V1.2 to V1.4); fault remained. Diagnosed as production defect in IPB internal Sensor B. Replaced IPB assembly, completed calibration, cleared fault. Vehicle delivered normally. Case indicates incoming parts quality issue.
Original source ↗
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.