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 — Seal U

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.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Open circuit or inter-turn short circuit in the left front outlet valve solenoid coil inside the IPB assembly: solenoid resistance deviates from the standard range (normally about 2-5 Ω), resulting in abnormal drive circuit detection.
  • 2Loose or corroded IPB to left front wheel speed sensor/valve body integrated wiring harness connector: Although C001100 indicates an internal valve drive fault, some models connect the IPB valve body and ECU as separate units. Backed-out or oxidized connector pins interrupt the drive signal.
  • 3Damaged internal solenoid valve driver chip (H-bridge driver) in the IPB ECU: 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, continuous high drive current triggers overcurrent protection, and the ECU records 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 if C001100 is a current fault. Check freeze frame parameters (vehicle speed, hydraulic pressure, battery voltage, etc.) to rule out false faults.
  • 2
    Wiring harness and connector visual inspection: Check the IPB assembly connector (usually located near the firewall) for looseness or water ingress. Measure continuity of the wiring harness from the connector to the valve body (resistance must be less than 1Ω). Inspect the pins for corrosion or backing 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 IPB terminal 30 constant power, terminal 15 ignition power, and ground wire voltages. Verify the voltages are within the 12-14V range. Unstable voltage may trigger false drive circuit 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 the following: 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 Perform a road test 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 Seal U Fault Codes
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.