NO
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 — Qin Plus

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
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 Qin Plus Fault Codes
B1108For 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.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.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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.