AU
C05C24B

The integrated motor drive unit of the IPB (Intelligent Power Brake) electro-hydraulic braking system triggers this DTC — Atto 8

Braking System

The integrated motor drive unit of the IPB (Intelligent Power Brake) electro-hydraulic braking system triggers this DTC.

When the internal temperature sensor of the brake assist motor (usually a permanent magnet synchronous motor or brushless DC motor) detects a temperature exceeding the safety threshold (generally 120°C-140°C, depending on software calibration), the ACM (Brake Assist Control Module) records this fault and enables thermal protection mode.

In this state, the system may limit or cut off motor assistance, resulting in a noticeably harder brake pedal and longer pedal travel.

The driver must build braking force entirely through manual effort.

This fault involves functional safety (ISO 26262).

The system illuminates the ABS/ESC warning lamp, may disable energy recovery, and forces the vehicle into limp-home mode.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Extreme operating conditions: Continuous high-frequency braking on long downhill sections, or repeated hard acceleration and deceleration while towing or fully loaded, causes the motor to operate continuously under high load and generate more heat than the cooling system can dissipate.
  • 2IPB control module software defect: Early software versions contain bugs in the thermal management strategy or motor drive PWM control logic, causing abnormal continuous motor operation or overheating under low load.
  • 3Brake system mechanical binding: Corroded brake caliper piston causing poor return, brake pad and disc drag, or partially blocked brake fluid line. This forces the motor to continuously output high torque to maintain pressure. The resulting excessive current causes overheating.
  • 4Motor assembly fault: Localized motor winding short circuit, permanent magnet demagnetization, or bearing wear causing increased friction, reducing efficiency, and generating abnormal heat.
  • 5Temperature monitoring circuit fault: Motor temperature sensor (NTC thermistor) drift, poor connector contact, or ACM internal sampling circuit fault, causing a false high-temperature warning.
What To Do
  • 1
    Connect the BYD VDS or Launch X-431 diagnostic tool and read the complete DTC list. Confirm if C05C24B is a current or history code and record the freeze frame data (focus on motor temperature, ambient temperature, brake pressure, and vehicle speed).
  • 2
    Check the IPB assembly software version against the BYD TSB. If a software upgrade solution exists for this fault code, update the ACM control module software to the latest version (such as V2.3 or higher released after 2023).
  • 3
    Perform the standardized brake system bleeding procedure: Follow the left rear - right rear - left front - right front sequence. Use the diagnostic tool to activate hydraulic pump bleeding to purge potential air locks from the lines (air locks cause the motor to spin freely and generate heat).
  • 4
    Check the mechanical condition of all four brake actuators: Raise the vehicle and check if the brake discs are overheated, the brake pads return smoothly, and the caliper slide pins are binding. Disassemble, clean, or replace the brake calipers if necessary.
  • 5
    Read the live data stream: Monitor the 'brake booster motor temperature' value under static and dynamic conditions. At normal room temperature, the value should closely match ambient temperature (±10°C). If the temperature remains above 80°C after the vehicle sits overnight, this indicates a sensor or wiring fault.
  • 6
    Check the IPB module electrical connections: measure the motor temperature sensor signal wire voltage at the 32-pin connector (typically 0.5V-4.5V corresponding to the temperature range), and check module ground point G102 for oxidation or looseness.
  • 7
    If the above steps fail and the fault recurs, replace the IPB integrated electro-hydraulic brake module assembly (part number HA2-3550100 or model-specific equivalent). After replacement, bleed the brake system and calibrate the pedal position sensor and longitudinal acceleration sensor.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i brake power assist failure during long downhill descent

✓
Brake pedal hardened after approximately 15 minutes of continuous braking on a long highway downhill. Instrument cluster displayed "Check Brake System." Retrieved DTC C05C24B (current code). Freeze frame showed motor temperature at 138°C. Brake calipers showed no sticking; brake pad thickness measured normal. Scan tool indicated IPB software version V1.8 (early version). Solution: Upgraded software to V2.3 (optimizes thermal management strategy). Advised customer to use forced EV mode combined with engine braking on long downhills to avoid continuous braking. No recurrence after 3 months of monitoring post-upgrade.
Original source ↗
BYD DTC AI Analysis

Sticking brake caliper causing continuous motor overheating

✓
Owner reported brake system warning lit after ~20 km city driving; fault cleared after parking to cool. Historic DTC C05C24B stored; current temperature normal. Right rear brake disc ran significantly hotter than the other three, with obvious drag. Disassembly revealed corroded caliper slide pins and pads not returning properly. Replaced right rear caliper and bracket. Cleaned slide pins and applied high-temp grease. Replaced brake fluid as well (old fluid at 3% water content). Post-repair: 30 km continuous road test, motor temp stayed below 65°C. Fault cleared.
Original source ↗
BYD DTC AI Analysis

Internal temperature sensor drift in IPB assembly causing false readings

✓
DTC C05C24B set immediately on cold start. Data stream showed motor temperature at -40°C (then jumping to 150°C), clearly inconsistent with actual conditions. IPB connector showed no corrosion; wiring continuity normal. Diagnosed as internal temperature sampling circuit fault or sensor failure in the ACM. Solution: Replaced IPB integrated electro-hydraulic brake module assembly. After replacement, performed standard installation (torque to 25Nm, apply thermal grease), completed bleeding and calibration. DTC cleared; data stream showed temperature matching ambient at 22°C.
Original source ↗
BYD DTC AI Analysis

Brake fluid contamination increased system internal resistance

✓
After water wading, the vehicle developed an intermittent C05C24B fault with excessive brake pedal travel. Inspection found milky brake fluid (water ingress/emulsification) and water content exceeding limits (>4%). Contaminated brake fluid increased the load on the IPB internal valve body and motor; operating current continuously exceeded 15A (normal <8A), causing rapid motor temperature rise. Solution: Thoroughly flushed the entire brake hydraulic system (3 cycles with new brake fluid), replaced the IPB assembly (internal valve body was contaminated), and replaced all rubber seals. Fault eliminated, current returned to normal range.
Original source ↗
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.