AU
C001100

DTC C001100 indicates a malfunction in the drive circuit of the internal left front wheel outlet solenoid valve within the Integrated Power Brake (IPB) system — Atto 3

Braking System

DTC C001100 indicates a malfunction in the drive circuit of the internal left front wheel outlet solenoid valve within the Integrated Power Brake (IPB) system.

This solenoid valve returns high-pressure brake fluid from the left front wheel brake cylinder to the reservoir during ABS/ESP activation to release wheel cylinder pressure.

A "drive fault" indicates the IPB ECU detects an open circuit, short circuit, or short to ground or power in the H-bridge circuit driving this solenoid valve, or it detects a drive current exceeding the calibrated threshold (typically 2-3A).

This fault prevents independent pressure release at the left front wheel, affecting ABS, ESC, AUTOHOLD, and Automatic Emergency Braking (AEB) functions.

The IPB enters a degraded mode, retaining conventional hydraulic braking while potentially limiting electronic brake assist.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Open circuit or inter-turn short circuit in the left front outlet valve solenoid coil inside the IPB assembly: solenoid valve resistance deviates from the standard range (normally approx. 2-5 Ω), causing abnormal drive circuit detection.
  • 2Loose or corroded connector on the integrated wiring harness from the IPB to the left front wheel speed sensor/valve body: Although C001100 indicates an internal valve drive fault, some models feature a split connection between the IPB valve body and the ECU. Backed-out or oxidized connector pins can interrupt the drive signal.
  • 3IPB ECU internal solenoid valve driver chip (H-bridge driver) damaged: Overvoltage, static electricity, or brake fluid ingress causes power MOSFET breakdown, preventing PWM drive signal output.
  • 4Severely contaminated brake fluid or excessive water content: Impurities cause the outlet valve spool to stick, sustained high drive current triggers overcurrent protection, and the ECU logs a drive fault.
  • 5IPB software version defect or calibration error: Incorrect drive PWM duty cycle calculation under specific operating conditions triggers a false circuit fault (update the IPB software to the latest version).
What To Do
  • 1
    Fault Confirmation and Freeze Frame Analysis: Use VDS or DMS1000 to read all fault codes and confirm C001100 is a current fault. Check freeze frame parameters, including vehicle speed, hydraulic pressure, and battery voltage, to rule out a false code.
  • 2
    Wiring harness and connector visual inspection: Check the IPB assembly connector (usually located near the firewall) for looseness or water ingress. Measure continuity from the connector to the valve body wiring harness (resistance should be less than 1Ω). Check the pins for corrosion or push-out.
  • 3
    Solenoid valve resistance measurement: Disconnect the IPB power supply, remove the IPB assembly, and measure the left front outlet valve solenoid coil resistance (refer to the workshop manual for the standard value, usually 2.0-5.0 Ω). If the resistance is infinite (open circuit) or less than 1 Ω (short circuit), this indicates an internal IPB fault.
  • 4
    Power supply and ground verification: Check the voltage at IPB terminal 30 (constant power), terminal 15 (ignition power), and the ground wire. Verify the voltage is within the 12-14V range. Unstable voltage may cause the drive circuit to trigger false faults.
  • 5
    IPB assembly replacement and matching: If diagnostics confirm an internal IPB fault, replace the IPB electro-hydraulic module assembly with ECU (verify the spare part number using the VIN). After replacement, perform: ① Bleed the brake system (use dedicated equipment to activate IPB bleeding mode); ② Calibrate the brake pedal position sensor; ③ Configure IPB parameters online (VIN, vehicle model code); ④ Road test the vehicle to verify ABS/ESC functions.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i: IPB internal solenoid coil open circuit

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At 80,000 km the ABS and ESC warning lights illuminated. Read DTC C001100 (current fault). Checked the IPB connector — no issues. Measured infinite resistance at the left front outlet valve (normal ~3.5 Ω), indicating an open circuit in the IPB internal solenoid coil. Replaced the IPB assembly and performed bleed and calibration; fault resolved. Root cause: coil fatigue fracture from long-term high-frequency solenoid operation.
BYD DTC AI Analysis

IPB Drive Circuit Corrosion Case After Water Wading

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Dashboard displayed "Braking System Fault" after driving through water. Retrieved DTCs C001100/C001104 (left front outlet/inlet valve drive fault). Disassembly revealed water inside the IPB connector; oxidised pins caused a short in the drive circuit. Fault persisted after cleaning and drying the connector. Internal IPB drive chip measured as burned out. Replaced IPB assembly and reinforced connector waterproofing.
BYD DTC AI Analysis

Software false positive caused intermittent C001100 fault.

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2021 Song PLUS DM-i. Customer reported occasional ABS warning light illumination during high-speed driving; the light extinguished after ignition-off. Diagnostic tool logged C001100 as a historical fault. Freeze frame data showed the vehicle was on rough road surfaces when the fault occurred. Wiring harness inspection found no damage. Solenoid valve resistance measured normal. TSB review revealed early IPB software had an overly strict solenoid valve drive current threshold calibration. Upgraded IPB software to V2.3. One-month follow-up showed no recurrence.
BYD DTC AI Analysis

Brake fluid contamination caused valve spool sticking

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One week after service, fault code C001100 appeared. Inspection found non-genuine brake fluid (incorrect DOT 4 specification) that was black and contaminated. IPB disassembly revealed the left front outlet valve spool stuck in the open position, causing continuous drive current overload; the ECU logged a protective fault. Replaced the IPB assembly, thoroughly flushed the brake lines, and filled with genuine DOT 4 LV brake fluid. Fault resolved.
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.