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 — Seal U

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.

The C001800 fault code on the Seal U indicates a medium-severity fault in the IPB brake control module’s left rear wheel inlet valve drive circuit. It may be caused by an open or shorted solenoid coil inside the electro-hydraulic module, or poor connector contact from water ingress, oxidation, or loose pins. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open or short circuit in the left rear inlet valve solenoid coil inside the 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 connection in the IPB module power supply or ground circuit causes insufficient drive voltage, leading the ECU to incorrectly detect a drive fault.
What To Do
  • 1
    Use VDS or a dedicated BYD diagnostic tool to read the complete fault codes 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 code.
  • 2
    Switch off the ignition, disconnect the IPB electro-hydraulic module wiring harness connector, and check the connector pins for corrosion, deformation, or signs of water ingress. If necessary, clean 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 workshop manual pinout diagram, typically the left rear inlet valve drive positive and negative terminals). Standard value: 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 ignition ON, measure voltage at the IPB connector power pin (should be 12V ± 0.5V), and check 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, the internal IPB ECU drive circuit is faulty. Replace the entire IPB electro-hydraulic brake assembly (part number depends on vehicle model, e.g., Song PLUS DM-i: 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

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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 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.