AU
C05CF00

DTC C05CF00 indicates the signal voltage or travel value from Master Cylinder Position Sensor B inside the IPB (Intelligent Integrated Braking System) falls outside the calibrated range (typically 0 — Atto 3

Braking System

DTC C05CF00 indicates the signal voltage or travel value from Master Cylinder Position Sensor B inside the IPB (Intelligent Integrated Braking System) falls outside the calibrated range (typically 0.5-4.5V or the corresponding physical travel limit).

This sensor features a dual-redundant design (Sensors A and B) to monitor brake master cylinder piston displacement in real time, enabling brake pedal travel interpretation, precise brake force distribution, and redundant safety cross-checking.

The IPB control unit sets this fault if Sensor B experiences an open circuit, short circuit, mechanical binding, or excessive signal deviation from Sensor A.

The fault may cause abnormal brake pedal feel (soft/hard), restricted regenerative braking, ABS/ESC system deactivation, and Automatic Emergency Braking (AEB) failure.

In extreme cases, it triggers limp mode (speed-limited driving).

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Hardware fault in IPB assembly master cylinder position sensor B: Damaged internal magnetoresistive element, failed Hall effect chip, or dry solder joint causing output signal drift or out-of-range condition.
  • 2Wiring harness and connector issues: poor contact in Sensor B power, signal, or ground circuits; oxidized or annealed pins; water ingress or moisture in the connector reducing insulation resistance; or wiring harness wear causing a short circuit.
  • 3Power supply and ground fault: Unstable constant power or ignition voltage to the IPB controller (below 11V or above 14V), or a loose ground wire bolt causing excessive contact resistance (>0.1Ω), resulting in sensor reference voltage drift.
  • 4Mechanical installation and hydraulic faults: Deformed IPB assembly mounting bracket resulting in coaxial misalignment between the sensor and the master cylinder piston, a binding brake master cylinder piston, or a failed return spring, causing the sensor to detect abnormal travel.
  • 5Software and calibration issues: An IPB controller software bug or lost/corrupted sensor calibration data causes signal interpretation errors (requires software upgrade or recalibration).
What To Do
  • 1
    Safety preparation and fault confirmation: Use VDS2000 or a dedicated BYD diagnostic tool to read all fault codes and freeze frame data. Record the vehicle speed, pedal travel, and sensor A/B voltage values at the time of the fault. Check the instrument panel warning light status and confirm whether the brake pedal force is normal.
  • 2
    Visual and basic inspection: Inspect the IPB assembly for impact damage and brake fluid leaks; verify the brake fluid level is between MAX and MIN, adding DOT4 brake fluid if necessary; check the IPB mounting bracket tightening torque (standard: 25±2 Nm) and mounting surface flatness.
  • 3
    Electrical system inspection: Disconnect the IPB wiring harness connector. Measure voltage at Pin30 (constant power) and Pin32 (ignition power); voltage must be 12V±0.5V. Measure resistance between ground Pin15, Pin16 and body ground; resistance must be <0.1Ω. Check sensor B power supply (typically 5V reference voltage) and signal wire continuity.
  • 4
    Sensor signal analysis: Connect the diagnostic tool and read the data stream. Compare the real-time values of master cylinder position sensors A and B. Values must change linearly and synchronously (difference <5%). If the sensor B signal fluctuates, remains fixed, or falls outside the 0.5-4.5V range, confirm a sensor fault.
  • 5
    Connector treatment: Inspect sensor wiring harness connector pins for oxidation, annealing, or water ingress. Clean with electrical contact cleaner, apply conductive grease (such as Stabillant 22), and verify the waterproof sealing ring is intact.
  • 6
    Calibration attempt: Clear the fault code, then perform 'Master Cylinder Position Sensor Calibration' (Sensor Calibration) and 'Zero Point Calibration'. Verify success. If calibration fails or the fault code reappears immediately, replace the IPB assembly.
  • 7
    IPB assembly replacement: If diagnostics confirm a faulty internal sensor, replace the Integrated Power Brake (IPB) system assembly (verify the part number for the specific vehicle model, e.g., 10245087-00 for Song PLUS DM-i). Before replacement, disconnect the 12V battery and wait 3 minutes to discharge residual high voltage.
  • 8
    Initialization after replacement: After installing the new IPB, perform the brake system bleeding procedure (use the diagnostic tool to activate motor pump bleeding; assist manually if necessary). Recalibrate the master cylinder position sensor, lateral acceleration sensor, and steering angle sensor.
  • 9
    Function verification: After completing calibration, conduct a road test to evaluate low-speed (<30km/h) and high-speed (>60km/h) braking performance. Verify normal operation of ABS, ESC, and AEB functions. Monitor the data stream to confirm sensor A/B signals synchronize and values are within the normal range.
Real-World Cases
BYD DTC AI Analysis

Seal DM-i: Oxidized IPB sensor pins caused abnormal signal

✓
Dashboard displayed "Check braking system", ABS/ESC fault lights illuminated, and brake pedal felt stiff. Scanned with VDS2000 and retrieved DTCs C05CF00 (Master cylinder position sensor B out of range) and C05CE00 (Sensor B voltage low). Checked IPB controller power and ground — both normal. Inspected master cylinder position sensor harness connector and found white oxidation on Pin 3 (signal) and Pin 4 (ground). Data stream showed Sensor B voltage jumping erratically between 0.2-4.8V while Sensor A varied linearly. Cleaned pins, applied conductive grease, and test drove; fault temporarily cleared but returned after 3 days. Replaced IPB assembly, performed brake bleeding and sensor calibration; fault permanently resolved.
Original source ↗
BYD DTC AI Analysis

Poor ground on Song PLUS DM-i caused Sensor B undervoltage and out-of-range condition

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Intermittent "Braking System Fault" warning on startup. Warning cleared after restart but reappeared while driving. Scanner detected C05CF00 and C05CE00 simultaneously. Brake fluid level normal, no leaks. IPB ignition supply voltage fluctuating 9–11V. Harness traced to IPB controller ground at left front longitudinal beam: retaining bolt corroded and loose, contact resistance 0.8Ω (spec <0.1Ω). Ground point cleaned to bare metal, new M8 bolt installed with anti-corrosion compound, tightened to 25Nm. Ground resistance retested at 0.03Ω. Fault codes cleared, no recurrence. No parts replaced.
BYD DTC AI Analysis

Han EV IPB mounting bracket deformation causes sensor signal mismatch

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While driving, the vehicle suddenly experienced power limitation. The dashboard displayed "Brake system fault", brake pedal travel increased, and the pedal required deep application to generate braking force. Read DTCs C05CF00 (Sensor B out of range) and C05D000 (A/B sensor mismatch). Data stream showed Sensor A at 15% piston position and Sensor B at 89%—the difference far exceeds the threshold (normal is <5%). Inspection found the IPB assembly mounting bracket had deformed slightly when the vehicle bottomed out. The IPB and brake master cylinder were misaligned, creating side force on the piston during movement. Adjusted the IPB mounting position, used feeler gauges to ensure the mounting surface gap was under 0.1mm, and tightened to the specified torque. Performed master cylinder position sensor calibration; the A/B sensor values synchronized and the fault cleared.
BYD DTC AI Analysis

Water ingress into Seal 06 DM-i sensor connector caused intermittent fault

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Owner reported the instrument cluster consistently displayed a brake system fault after rain or washing, clearing once dry. Inspection found the IPB mounted low with a degraded waterproof seal on the sensor harness connector, allowing water ingress. The sensor B signal line measured only 0.5 MΩ insulation resistance (specification: >10 MΩ), causing signal leakage to ground and pulling the voltage below the lower limit. Dried the connector with compressed air, replaced the waterproof seal, and applied waterproof sealant to the damaged section of the wiring harness corrugated tube. Advised the owner to avoid directing high-pressure washers at the IPB area; the fault has not recurred.
BYD DTC AI Analysis

Tang DM-p IPB software false positive causing intermittent C05CF00

✓
No actual braking fault, but the brake warning light on the dash came on intermittently with DTC C05CF00. Checked sensor wiring, power supply and ground — all normal. Data stream showed Sensor B signal within normal range but with occasional instantaneous spikes (<50ms). Consulted BYD technical bulletin: confirmed as IPB controller software V1.02 bug. Under specific road conditions (continuous bumpy roads), the signal sampling filter algorithm defect causes false positives. Upgraded IPB software to V1.05, cleared historical DTCs, performed sensor calibration, and monitored for 1 week — no recurrence.
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.