AU
C059100

This DTC indicates the supply voltage to the IPB (Integrated Power Brake) internal brake booster motor is below the normal operating threshold set by the ECU (typically below 9V or 75% of the nominal value) — Atto 8

Braking System

This DTC indicates the supply voltage to the IPB (Integrated Power Brake) internal brake booster motor is below the normal operating threshold set by the ECU (typically below 9V or 75% of the nominal value).

The IPB system uses a vacuum-free electro-hydraulic assist design.

A DC motor drives a hydraulic pump to build brake assist pressure.

When motor voltage drops too low, the ECU limits assist torque output to protect hardware.

This results in a significantly harder brake pedal, longer pedal travel, and increased braking distance.

The IPB internal power management module triggers this fault by monitoring the motor drive circuit voltage in real time.

Possible causes include an abnormal external power supply, excessive wiring voltage drop, poor connector contact, or a failed IPB internal DC-DC converter or motor drive circuit.

A persistent fault causes the IPB to enter Limp Home mode, limits vehicle speed, and illuminates multiple system warning lights.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Poor connection, oxidation, or burnt fuse holder in the IPB assembly main power circuit (constant +B or IGN power) causes voltage drop under high-current conditions (especially at motor startup, when current reaches 30–50 A).
  • 2IPB internal power management module (DC-DC converter or pre-driver circuit) fault, failing to output the stable 12V/24V voltage required to drive the motor (some models use a boost drive).
  • 3Low-voltage battery aging (increased internal resistance) or unstable DC-DC converter output causes the vehicle 12V system voltage to drop below 11V, triggering IPB low-voltage protection.
  • 4Water ingress, corrosion, pin back-out, or seal failure at the IPB wiring harness connector (typically a large 48-pin or 64-pin plug), causing increased contact resistance and a voltage drop.
  • 5Internal short circuit, demagnetization, or excessive carbon brush wear in the brake booster motor causes an abnormal increase in operating current, dropping the supply voltage or triggering the ECU overcurrent/undervoltage protection logic.
What To Do
  • 1
    Read freeze frame and fault conditions: Use the BYD dedicated diagnostic tool (VDS or X-431) to read the C059100 freeze frame data. Record the motor voltage, vehicle speed, brake pedal travel, SOC status, and ambient temperature at the time of the fault. Determine whether the fault is intermittent (intermittent voltage drop) or persistent.
  • 2
    Check the external power supply system: Measure the voltage drop across the IPB power supply fuse in the front compartment distribution box (usually F1/40A or F2/60A; refer to the vehicle wiring diagram). With the vehicle started, measure the voltage between IPB connector B (power connector) Pin 1/2 (+B) and body ground. The voltage must remain stable at 13.5-14.5V. Check the fuse holder for burning or terminal spread.
  • 3
    Check the ground circuit: Verify the tightening torque of the IPB ground point (typically G401 on the left front longitudinal rail or G402 near the battery negative terminal) is 9–12 N·m. Remove paint and oxidation from the ground point. Measure the voltage drop and resistance between the IPB connector ground pin and the battery negative terminal. The voltage drop must be less than 0.1 V, and the resistance must be less than 1 Ω.
  • 4
    Measure motor and circuit resistance: Disconnect all IPB connectors. Use a multimeter to measure the winding resistance between the brake booster motor power supply pins (normal value approximately 0.8-2.5Ω at 20°C). Verify the motor power supply circuit insulation resistance to ground is greater than 20MΩ. Inspect the wiring harness shielding for damage causing an intermittent short circuit.
  • 5
    Software update and assembly replacement: If circuit measurements are normal, update the IPB ECU software to the latest version (early software versions set voltage sampling thresholds too strictly). If the fault persists, replace the IPB with ECU assembly. After replacement, perform: ① brake system bleeding (use the diagnostic tool to activate the motor pump for bleeding) ② longitudinal acceleration sensor calibration ③ steering angle sensor calibration ④ road test to verify brake assist function.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DMi: Water ingress and corrosion in IPB connector after wading caused low voltage

✓
After driving through water, the instrument panel showed ABS/ESC warning lights. Read DTC C059100 (brake booster motor voltage low). Found the IPB mounted beneath the left front chassis rail with a perished connector seal; inside showed water staining and green corrosion. Disassembled the connector, cleaned the pins with ethanol, applied conductive grease and replaced the seal. Motor supply voltage returned to normal. Cleared the fault codes and road-tested for one week with no recurrence.
BYD DTC AI Analysis

Sudden brake pedal hardening and power assist failure while driving.

✓
Owner reported brake pedal suddenly hardened during high-speed driving, requiring heavy effort to decelerate; brake system warning light illuminated. Scan tool read DTC C059100; freeze frame showed motor voltage at 7.2V during the fault. Found burn marks on IPB supply fuse F1/40A blades; fuse holder internal spring clips had lost elasticity, causing poor contact. Replaced fuse and holder, tightened ground point. Fault resolved.
BYD DTC AI Analysis

C059100 still present after replacing low-voltage battery on Yuan Plus

✓
Vehicle set DTC C059100. The shop replaced the 12V battery but the code remained. Deep inspection found soft breakdown in the IPB internal brake booster motor drive MOSFET, causing abnormal static current draw (normal <0.3A, measured 1.8A) that dragged system voltage low. Replaced the IPB assembly with ECU, bled the brakes and calibrated sensors. Motor operating voltage returned to 13.8V; fault completely resolved.
BYD DTC AI Analysis

Han EV IPB internal DC-DC converter intermittent fault

✓
Brake system warning light came on intermittently with DTC C059100. External power supply tested normal. Suspected internal IPB power management module failure. Disassembled IPB assembly (maintain dust/water protection). Found capacitor leakage around the DC-DC converter chip (typically Mornchip or TI solution) on the internal PCB, causing unstable output voltage. Replaced IPB assembly; fault cleared. Returned old part to factory for analysis.
BYD DTC AI Analysis

Qin PLUS DM-i wiring harness chafing against body causing intermittent low voltage

✓
While driving on rough surfaces, the brake warning light illuminated intermittently. The scan tool retrieved historic DTC C059100. Inspection revealed the IPB wiring harness rubbing against the sheet metal edge at the front left chassis rail; abraded insulation caused an intermittent short to ground on the power supply line, producing a voltage drop. Repaired the harness using double-layer heat shrink tubing, rerouted and secured the harness (added corrugated tube protection), and repositioned cable ties to avoid sharp edges. Fault resolved.
Other Atto 8 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.