AU
C05D000

This DTC indicates the signal difference between dual redundant channels A and B of the Master Cylinder Position Sensor inside the IPB (Intelligent Integrated Braking System) exceeds the diagnostic threshold — Qin Plus

Braking System

This DTC indicates the signal difference between dual redundant channels A and B of the Master Cylinder Position Sensor inside the IPB (Intelligent Integrated Braking System) exceeds the diagnostic threshold.

For functional safety (ISO 26262), the IPB uses a dual-channel redundant design to monitor brake master cylinder piston travel.

When the difference between the two signals continuously exceeds the calibrated value (typically 5%-10%), the system determines the sensor signal is implausible.

This fault triggers the brake system limp-home mode, potentially causing a loss of electronic brake assist, a hard brake pedal, ABS/ESC deactivation, and illuminating multiple system warning lights.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Master cylinder position sensor internal circuit fault or signal drift causing inconsistent dual-channel outputs.
  • 2Loose mechanical connection between sensor and master cylinder piston, abnormal clearance, or offset installation position
  • 3Water ingress, oxidation, or loose pins at the IPB wiring harness connector (especially the 32-pin or 48-pin main plug) causing signal crosstalk.
  • 4IPB control unit internal signal acquisition circuit fault (ADC conversion error or power supply interference)
  • 5Brake master cylinder mechanical binding or poor piston return causing a deviation between the actual position and the sensor reading.
What To Do
  • 1
    Use VDS or a BYD dedicated diagnostic tool to read the complete DTC list and freeze frame data. Record vehicle speed, pedal travel, and channel A/B raw signal values at the time of the fault.
  • 2
    Verify the brake fluid level is normal. Inspect the IPB and lines for leaks, deformation, or external damage.
  • 3
    Disconnect the IPB wiring harness connector and check the pins for corrosion, water ingress, or recession. Measure the sensor power supply (5V±0.25V) and ground (<0.1Ω).
  • 4
    Use an oscilloscope or multimeter to monitor the signal voltage curves of master cylinder position sensor channels A and B relative to pedal travel. Verify both signals change in the same direction and the difference between them is within the allowable range.
  • 5
    Check the IPB mechanical mounting bolt torque (usually 8-12 Nm) and verify the module-to-master cylinder connection is secure.
  • 6
    If diagnostics confirm a sensor fault and the sensor cannot be replaced separately, replace the complete IPB (Intelligent Integrated Braking System) assembly. The new module must match the vehicle configuration.
  • 7
    Perform the brake system bleeding procedure (use the diagnostic tool to activate motor bleeding in combination with conventional bleeding).
  • 8
    Perform master cylinder position sensor zero-point calibration (Master Cylinder Position Calibration) and pedal travel learning.
  • 9
    Clear the fault code, perform static and dynamic tests, and verify the A/B channel signal difference is within the normal range (<3%).
Real-World Cases
BYD DTC AI Analysis

Song Plus DM-i sensor connector corroded after water ingress

✓
Brake system warning light illuminated after driving through water. Read DTC C05D000. Found water inside the IPB harness connector (located above the left front wheel arch). Pins 3 and 4 (sensor A/B signals) had green corrosion. Cleaned the connector and applied conductive protectant; signal discrepancy temporarily cleared but returned after one week. Replaced the IPB harness connector and waterproofed the connection to completely eliminate the fault.
BYD DTC AI Analysis

Seal master cylinder position sensor internal drift

✓
Customer reported excessive free play at the beginning of brake pedal travel and a "Brake System Fault" warning on the dashboard. Live data showed sensor A voltage rising from 0.5V to 2.8V and sensor B from 0.5V to only 2.1V when depressing the pedal—a 25% difference (normal: <5%). Wiring checked normal, confirming an internal IPB sensor fault. Replaced the IPB assembly and completed calibration. The signal difference between the two channels returned to 1.2%, clearing the fault.
BYD DTC AI Analysis

Wiring harness wear on Qin PLUS caused intermittent fault

✓
ABS warning light illuminated intermittently on rough roads. DTC C05D000 stored as history code. Inspection revealed chafing on IPB-to-body harness transition at firewall mounting clip; Sensor B signal wire insulation worn through, intermittently shorting to shield. Repaired harness and re-secured routing. Fault did not recur over 50 km of continuous road testing.
BYD DTC AI Analysis

Yuan Plus: IPB replaced without calibration, causing fault

✓
The workshop replaced the IPB assembly without performing sensor zero-point calibration. After driving 10 km, the vehicle set fault code C05D000. Live data showed signal values of 0.3 V and 0.8 V for channels A and B respectively at standstill (theoretical value: 0.5 V ± 0.1 V). Executing 'Master Cylinder Position Sensor Zero-point Calibration' and 'Pedal Min/Max Position Learning' with a diagnostic scanner automatically cleared the fault code and restored normal system operation.
Other Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus overview →
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.