AU
C001800

DTC C001800 indicates the IPB (Intelligent Power Brake) electro-hydraulic control module detects an abnormal drive circuit for the left rear wheel inlet valve — Atto 3

Braking System

DTC C001800 indicates the IPB (Intelligent Power Brake) electro-hydraulic control module detects an abnormal drive circuit for the left rear wheel inlet valve.

This is a hardware-level fault.

During self-check or operation, the ECU detects an open circuit, a short circuit (to ground or power), or a driver chip fault in the left rear inlet valve solenoid coil drive circuit.

The inlet valve is a key component of the ABS/ESC Hydraulic Control Unit (HCU) and controls the hydraulic passage between the brake master cylinder and the left rear wheel brake cylinder.

This fault prevents the left rear wheel from participating in ABS, ESC, and regenerative braking coordination.

In extreme cases, it may cause left rear wheel brake failure or brake drag, severely compromising driving safety.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Open or short circuit in left rear inlet valve solenoid coil inside IPB electro-hydraulic module (abnormal resistance; normal: 2-5 Ω)
  • 2Water ingress, oxidation, or loose pins in the IPB module wiring harness connector (32-pin or 48-pin connector) causing poor contact in the drive signal circuit.
  • 3Solenoid valve driver chip (MOSFET or dedicated driver IC) on the internal IPB ECU circuit board is burnt out or has a cold solder joint.
  • 4Severely contaminated brake fluid (containing metal debris or moisture) causes the inlet valve spool to stick, resulting in abnormal drive current that triggers protection.
  • 5Poor contact in the IPB module power supply or ground circuit results in insufficient drive voltage, which the ECU incorrectly identifies as a drive fault.
What To Do
  • 1
    Use VDS or the BYD dedicated diagnostic tool to read the complete fault code and freeze frame data. Verify vehicle speed, hydraulic pressure, system voltage, and other parameters at the time of the fault to rule out a false fault.
  • 2
    Turn off the ignition switch. Disconnect the IPB electro-hydraulic module wiring harness connector. Check the connector pins for corrosion, deformation, or water ingress. If necessary, clean the pins with electrical contact cleaner and apply conductive grease.
  • 3
    Measure the left rear inlet valve solenoid resistance: Use a multimeter to measure the corresponding pins on the IPB wiring harness side (refer to the repair manual pinout, typically the left rear inlet valve drive positive and negative pins). The standard value is 2.0-5.0 Ω. If the resistance is infinite (open circuit) or close to 0 Ω (short circuit), the internal IPB solenoid valve is faulty.
  • 4
    Check the IPB power supply and ground: With the ignition ON, measure the voltage at the IPB connector power pin (should be 12V±0.5V), and check the resistance between the ground pin and the vehicle body ground (should be less than 1Ω).
  • 5
    If all above checks are normal but the fault code remains, the IPB internal ECU drive circuit is faulty. Replace the complete IPB electro-hydraulic brake assembly (part number depends on the vehicle model, e.g., 6A-3505010-X for Song PLUS DM-i). After replacement, perform the bleeding procedure, ESC calibration, and longitudinal acceleration sensor calibration.
Real-World Cases
BYD DTC AI Analysis

Left rear fuel inlet valve driver fault after driving through water — Song PLUS DM-i

✓
A 2021 Song PLUS DM-i with 32,000 km came in with the ABS and ESC warning lights on. The diagnostic scanner read DTCs C001800 (left rear inlet valve drive fault) and U0121 (lost communication with ABS). Inspection revealed the vehicle had been driven through water. The IPB module sits near the left front longitudinal member; the 32-pin harness connector showed water ingress and verdigris inside. Removed the connector, cleaned it with anhydrous alcohol, dried it, applied electronic protective silicone grease and reinstalled it. The fault cleared temporarily. One week later the fault returned. Resistance measurements on the solenoid valve showed intermittent readings. Replaced the IPB electro-hydraulic module assembly, bled the brake system and performed calibration. Fault permanently resolved.
BYD DTC AI Analysis

Brake fluid replacement on Han EV triggered C001800

✓
2022 Han EV: ABS light stayed on after a repair shop changed the brake fluid. Scanned DTC C001800. Found the shop used non-DOT4-standard brake fluid. Improper bleeding let air into the IPB hydraulic unit. Contamination jammed the left rear inlet valve spool, causing abnormal drive current and an ECU drive fault. Fix: Replaced with fresh BYD-spec DOT4 brake fluid. Executed the 'Brake Fluid Replacement' routine with the diagnostic tool, then bled and flushed the hydraulic circuit repeatedly. Cleared codes and completed ESC dynamic calibration.
BYD DTC AI Analysis

Tang DM-i IPB internal solenoid valve coil open circuit

✓
2021 Tang DM-i. While driving, the instrument cluster suddenly displayed 'Braking System Fault', with the ABS and ESC warning lights illuminated. Read DTCs; only C001800 present as a current fault. Disconnected the IPB wiring harness and directly measured the left rear inlet valve solenoid resistance (via the pinout on the IPB assembly). Measured infinite resistance (normal approximately 3.5Ω) and determined an open circuit in the IPB internal solenoid coil. Internal hardware damage to the IPB assembly; the solenoid is not separately repairable. Replaced the IPB electro-hydraulic module assembly, performed the standard bleed procedure (requires a scan tool to trigger the motor pump bleed), and calibrated the steering angle sensor and longitudinal acceleration sensor. 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.