AU
C05CC00

DTC C05CC00 indicates the master cylinder piston position sensor A signal in the IPB (Integrated Power Brake) exceeds the ECU-calibrated valid range (typically 0 — Seal U

Braking System

DTC C05CC00 indicates the master cylinder piston position sensor A signal in the IPB (Integrated Power Brake) exceeds the ECU-calibrated valid range (typically 0.5V-4.5V or the corresponding physical travel range).

This Hall effect sensor monitors brake master cylinder piston displacement in real time to calculate driver braking intent, control brake booster motor torque distribution, and coordinate electro-hydraulic blended braking.

The IPB module sets this fault when an open circuit, short circuit, or short to power/ground causes the sensor signal voltage to exceed limits, or when actual piston displacement exceeds the physical travel range detectable by the sensor.

Upon fault trigger, the vehicle may enter brake backup mode (no assist or limited assist).

The system disables regenerative braking, may degrade ABS/ESP functions, and illuminates the brake system warning lamp on the instrument cluster.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Loose or corroded wiring harness connector: The wiring harness between the IPB module and the master cylinder sensor routes through a high-temperature area in the engine compartment. This exposure causes terminal pin back-out, oxidation, or poor sealing, resulting in intermittent signal interruption or drift.
  • 2Sensor body damage: Hall element aging, internal short circuit, or detached magnetic ring causes the output signal voltage to remain fixed at an extreme value (near 0V or 5V).
  • 3IPB control unit reference voltage abnormal: Module internal 5V regulator circuit fault causes excessively high or low sensor supply voltage.
  • 4Mechanical overtravel: Internal binding in the brake master cylinder, poor piston return, or incorrect installation causes the actual piston position to exceed the sensor's calibrated physical detection range.
  • 5Electromagnetic interference or software bug: High-voltage system electromagnetic interference causes transient signal anomalies, or the IPB control software is overly sensitive when evaluating signal plausibility.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS2000/3000) to read the fault codes and freeze frame data. Record the vehicle speed, brake pedal travel, and sensor voltage values at the time of the fault to confirm if the fault is intermittent.
  • 2
    Check the wiring harness connector between the IPB electro-hydraulic module and the brake master cylinder sensor (usually located near the ABS pump assembly). Inspect the terminals for backing out, burning, or water corrosion, and measure the terminal retention force to verify it is normal.
  • 3
    Disconnect the sensor connector. Measure the IPB-side supply voltage (normal: 5 V ± 0.25 V) and ground resistance (< 1 Ω). Use an oscilloscope to check the signal wire for normal PWM or analog voltage output.
  • 4
    Connect the sensor and monitor the Sensor A signal voltage in real time while pressing the brake pedal. The voltage should change linearly with pedal travel (typically 0.5-4.5V). If the signal jumps or falls outside this range, replace the sensor.
  • 5
    Check the brake master cylinder for smooth mechanical movement. Remove the master cylinder and inspect the piston for binding or scratches, and the magnetic ring for detachment or damage.
  • 6
    If the wiring and sensor are normal but the fault persists, check the IPB control unit software version and update to the latest version if necessary. If a hardware fault is present, replace the IPB electro-hydraulic assembly.
  • 7
    After replacing the part, perform the IPB system bleeding procedure (use a dedicated diagnostic tool to activate motor bleeding), and perform master cylinder position sensor zero-point calibration and brake pedal position learning.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i wiring harness poor contact causing intermittent signal out of range

✓
ABS and ESP warning lights intermittently lit up. Read DTC C05CC00 (current) and history codes. The fault triggered easily on rough roads. Freeze frame showed sensor voltage at 4.98V (exceeding upper limit). Removed the IPB module connector and found slight terminal spread and oxidation on pin 14 (sensor A signal). Repair: Used special tools to restore pin retention, applied conductive grease, cleared the codes, and road tested for one week with no recurrence. This case shows that high-temperature vibration in the engine bay increases wiring harness contact resistance, causing signal drift.
Original source ↗
BYD DTC AI Analysis

Seal 06 DM-i: Abnormal sensor supply voltage caused out-of-range fault

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The new vehicle had driven 3000 km when the instrument cluster displayed a "Brake System Fault" warning and the brake pedal became stiff. A scan tool retrieved DTC C05CC00. Technicians measured Sensor A supply voltage at 6.2V (outside the normal 5V range), with signal voltage at 5.0V that did not change with pedal movement. After disconnecting the sensor, 6.2V remained at the IPB side supply, indicating an internal 5V voltage regulator circuit fault in the IPB module. Because the IPB electro-hydraulic module is a sealed unit, technicians replaced the IPB assembly to clear the fault, then bled the system and performed calibration. This case shows that internal power supply faults cause abnormal sensor signal references.
Original source ↗
BYD DTC AI Analysis

Han DM-i brake master cylinder magnetic ring detached, causing mechanical over-travel

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After driving through water, the instrument cluster displayed a brake system fault. Read DTC C05CC00; the DTC would not clear. Disassembly found the master cylinder piston position sensor magnetic ring had detached after water ingress swelled the aged seal. The ring lodged in the master cylinder's non-working area, causing the sensor to detect abnormal magnetic field strength with output voltage out of range (measured 0.2V, below lower limit). Replaced the brake master cylinder assembly (including sensor and magnetic ring) and resealed the wiring harness. Fault resolved. Sensor mechanical installation and waterproof sealing are critical.
BYD DTC AI Analysis

BYD Song Pro DM-i software calibration fault caused false out-of-range warnings

✓
Hard braking triggered an instrument cluster warning and DTC C05CC00. Freeze frame showed 4.6V—only slightly above the calibration threshold. No physical damage to the wiring harness or sensor; signal range measured 0.4-4.6V. Software plausibility thresholds too strict. Updated IPB control software to latest version (confirm version number for specific model year) and performed sensor calibration. Fault did not return. This software calibration edge case requires data analysis and software upgrade to resolve.
Other Seal U Fault Codes
B1108For 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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.