AU
C05C24B

The integrated motor drive unit of the IPB (Intelligent Power Brake) electro-hydraulic braking system triggers this DTC — Atto 3

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 3
  • 1Extreme operating conditions: Continuous high-frequency braking on long downhill sections, or repeated hard acceleration and deceleration while towing or fully loaded, causing the motor to operate continuously under high load and generate heat exceeding cooling capacity.
  • 2IPB control module software defect: A bug in the thermal management strategy or motor drive PWM control logic of early software versions causes 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 partial brake fluid line blockage. These conditions force the motor to continuously output high torque to maintain pressure, drawing excessive current and causing overheating.
  • 4Motor assembly fault: Localized short circuit in motor windings, permanent magnet demagnetization, or bearing wear causing increased friction, resulting in reduced efficiency and abnormal heat generation.
  • 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, read the complete DTC list, determine whether C05C24B is a current or history code, and record the freeze frame data (focus on parameters such as motor temperature, ambient temperature, brake pressure, and vehicle speed).
  • 2
    Check the IPB assembly software version. Refer to 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 standard brake system bleeding procedure: Use the diagnostic tool to activate hydraulic pump bleeding in the sequence of left rear, right rear, left front, and right front. Purge any air locks from the lines (air locks cause the motor to free-spin and generate heat).
  • 4
    Check the mechanical condition of the four-wheel 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 caliper if necessary.
  • 5
    Read live data stream: Monitor the 'brake booster motor temperature' value under static and dynamic conditions. At normal room temperature, the value should match ambient temperature (±10°C). If the displayed temperature remains above 80°C after the vehicle sits overnight, diagnose a sensor or wiring fault.
  • 6
    Check IPB module electrical connections: Measure the motor temperature sensor signal wire voltage at the 32-pin connector (normally 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 persists, 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 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.