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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 — Qin Plus

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.

The C05CD00 fault code on the Qin Plus indicates the master cylinder piston position sensor B signal voltage inside the IPB braking system is too high. Severity is medium, as braking assist, energy recovery, ABS, or ESP functions may be reduced. Common causes include a faulty integrated position sensor or a short to power in the sensor wiring. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Damaged master cylinder position sensor B inside the IPB electro-hydraulic module: The sensor is highly integrated with the IPB. A faulty 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 driving through water or high-pressure car washing.
  • 4IPB power supply fault: 12V supply voltage to the IPB module increases abnormally (e.g., alternator regulator fault), causing the internal sensor supply reference to shift.
  • 5Software calibration error: In rare cases, incorrect Sensor B voltage threshold calibration in the IPB control software or missing calibration data triggers a false fault (reflash the software to resolve).
What To Do
  • 1
    Safety confirmation and initial inspection: Verify 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). Use the VDS2000/VDS6000 diagnostic tool to read all fault codes and record freeze frame data. Verify C05CD00 is a current fault, not a history fault.
  • 2
    Data stream analysis: Access the IPB system and read the live voltage data for Master Cylinder Position Sensor B. Check if the voltage remains continuously above 4.8V (normal range is usually 0.5-4.5V). Check the Sensor A voltage for comparison. If Sensor A is normal and Sensor B is abnormal, this initially rules out a common power supply issue.
  • 3
    Wiring harness and connector inspection: Disconnect the IPB module low-voltage plug (usually located near the firewall). Verify the plug sealing ring is intact and inspect the pins for water corrosion (blue-green oxide) or burn marks. Using a multimeter, 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 contacting the vehicle body power wire.
  • 4
    Sensor and module inspection: Measure the 5V reference voltage for Sensor B at the IPB connector (4.9-5.1V). If the supply voltage 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 no short circuit.
  • 5
    IPB assembly replacement: Master cylinder position sensor B is integrated inside the IPB and cannot be replaced separately. Replace the complete IPB electro-hydraulic module assembly. Before replacement, power down the old module, disconnect the negative battery 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 execute: 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 no fault code recurrence.
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

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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

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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 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.