AU
C05CA00

DTC C05CA00 indicates the IPB (Intelligent Integrated Braking System) electro-hydraulic control module detects the signal voltage from Brake Master Cylinder Piston Position Sensor A exceeds the normal upper limit (typically >4 — Qin Plus

Braking System

DTC C05CA00 indicates the IPB (Intelligent Integrated Braking System) electro-hydraulic control module detects the signal voltage from Brake Master Cylinder Piston Position Sensor A exceeds the normal upper limit (typically >4.8V, normal range is 0.5-4.5V).

This Hall-effect or potentiometer-type position sensor monitors the travel position of the primary brake master cylinder piston in real time.

It provides the IPB ECU with precise pedal depth and hydraulic build-up rate data, enabling regenerative braking, brake assist adjustment, and ESC intervention.

High voltage indicates a short to power in the sensor signal circuit, an internal sensor short, an ECU sampling circuit fault, or an abnormally high reference voltage.

This fault distorts brake pedal travel recognition, triggers the brake system degraded mode (loss of regenerative braking, pure hydraulic braking), and restricts ABS/ESC functions.

3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Damaged sensor wiring harness insulation causes the signal wire to short to +B (common in high-temperature engine compartment areas or frequent bending points near the steering column).
  • 2Short circuit in the internal Hall element or thick-film resistor of the brake master cylinder piston position sensor (sensor body fault)
  • 3A fault in the internal 5V reference power supply voltage regulator circuit of the IPB electro-hydraulic module causes abnormally high output voltage.
  • 4Water ingress and corrosion in the sensor connector causing a short circuit between pins (especially common after washing the vehicle or driving through water).
  • 5The signal wiring harness between the ECU and the sensor chafes against the power wiring harness within the body harness.
What To Do
  • 1
    Connect the VDS diagnostic tool to read the fault code and freeze frame data. Confirm the vehicle speed, pedal travel, and voltage values when the fault occurred. Clear the fault code and road test the vehicle to verify if the fault is intermittent.
  • 2
    Disconnect the connector between the IPB electro-hydraulic module and the brake master cylinder position sensor. Inspect the pins for corrosion, push-out, or burning. Measure the voltage between the sensor-side power supply pin (usually PIN1) and ground (PIN3) to confirm a stable 5V (normal 4.9-5.1V). If the voltage is >5.3V, check the ECU power supply circuit.
  • 3
    Measure the resistance between the sensor signal wire (PIN2) and ground to check for a short to power (resistance <1Ω and continuity with the power wire). If normal, measure the sensor static resistance. The normal range is typically 2-5kΩ. If the resistance is abnormal or indicates a short circuit, replace the brake master cylinder position sensor.
  • 4
    Inspect the wiring harness routing, focusing on the firewall pass-through, under the steering column, and harness securing points near the IPB module. Check for damaged insulation or signs of chafing. If necessary, open the corrugated conduit to inspect the internal wires.
  • 5
    If the wiring harness and sensor are normal, measure the resistance to ground and the voltage at the IPB module signal input terminal. If the signal voltage remains >4.8V after disconnecting the sensor, the IPB electro-hydraulic module internal ADC sampling circuit or signal conditioning circuit is faulty. Replace the IPB assembly and perform the bleeding and calibration procedures.
  • 6
    After repairing the wiring harness or replacing the sensor, reconnect all connectors. Use the diagnostic tool to perform the 'Brake Pedal Position Sensor Calibration' and 'IPB System Bleeding' procedures. Verify the fault code does not return and the brake pedal travel data stream changes linearly (0-100%) with pedal application.
Real-World Cases
BYD DTC AI Analysis

BYD Song PLUS DM-i brake warning light illuminated after driving through water

✓
After driving through water approximately 30 cm deep, the ABS and ESC warning lights illuminated on the instrument panel. Read DTCs C05CA00 (Master Cylinder Position Sensor A Voltage High) and C05CB00 (Voltage Low) as intermittent faults. Inspection found the IPB module above the left front wheel arch; its connector seal had deteriorated, letting water in and shorting the sensor power and signal pins. Cleaned and blow-dried the connector, applied conductive adhesive, and replaced the waterproof seal ring. Fault cleared. Recommend inspecting the wheel arch liner seals.
BYD DTC AI Analysis

Seal 6 DM-i braking system abnormality after accident repair

✓
After right-front collision repairs, the vehicle immediately set DTC C05CA00 at startup with a hard brake pedal and regenerative braking disabled. Inspection revealed the brake master cylinder sensor harness—rerouted during the accident repair—was not secured per factory routing and rubbed against the battery positive cable in the engine bay. Chafed insulation allowed the signal wire to short to 12V. Repaired the harness (replaced with 0.5mm² shielded wire), separated the high- and low-voltage harness routing, and cleared the fault codes. Brake system returned to normal.
BYD DTC AI Analysis

Internal fault in BYD Dolphin IPB module caused false alerts.

✓
No accident or water damage history. Brake warning light illuminated intermittently. Diagnostic scan revealed historic DTC C05CA00. Measured sensor supply voltage at 5.2V (normal). Signal line static voltage was 5.1V (abnormal; should read approx. 2.5V). Disconnected the sensor and measured its internal resistance — normal. Applied external 5V power directly to the sensor; signal output tested normal. Determined the IPB electro-hydraulic module's internal 5V reference voltage regulator was faulty (output measured 5.8V). Replaced the IPB assembly, performed system calibration, and fully resolved the fault.
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.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.