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 8

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 8
  • 1Open or short circuit in the left rear inlet valve solenoid coil inside the IPB electro-hydraulic module (abnormal resistance; normal: 2-5Ω)
  • 2Water ingress, oxidation, or loose pins at the IPB module wiring harness connector (32-pin or 48-pin), causing poor contact in the drive signal circuit.
  • 3Solenoid valve driver chip (MOSFET or dedicated driver IC) on the IPB internal 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, generating abnormal drive current that triggers protection.
  • 5Poor contact in the IPB module power or ground circuit results in insufficient drive voltage, causing the ECU to falsely detect 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. Confirm parameters such as vehicle speed, hydraulic pressure, and system voltage at the time of the fault to rule out a false code.
  • 2
    Switch off the ignition and disconnect the IPB electro-hydraulic module wiring harness connector. Inspect the connector pins for corrosion, deformation, or signs of 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). 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 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 body ground (should be less than 1Ω).
  • 5
    If all above checks are normal but the fault code persists, diagnose an IPB internal ECU drive circuit fault. Replace the complete IPB electro-hydraulic brake assembly (part numbers vary by model; e.g., Song PLUS DM-i uses 6A-3505010-X). 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 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.