AU
C001900

DTC C001900 indicates a malfunction in the drive circuit or mechanical components of the Rear Left Outlet Valve inside the IPB (Integrated Power Brake) hydraulic control unit — Seal U

Braking System

DTC C001900 indicates a malfunction in the drive circuit or mechanical components of the Rear Left Outlet Valve inside the IPB (Integrated Power Brake) hydraulic control unit.

During ABS/ESC operation, this solenoid valve controls brake fluid return from the left rear wheel cylinder to the low-pressure accumulator or reservoir to precisely regulate wheel cylinder pressure.

The ECU detects an abnormal valve drive current (open circuit, short circuit, or short to ground/power) or mechanical sticking of the valve spool, preventing the IPB from releasing pressure at the left rear wheel.

This fault triggers ESP system degraded mode and may limit ABS, ESC, energy recovery, and automatic emergency braking functions.

The system usually retains conventional hydraulic braking (depending on the IPB failsafe strategy).

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open circuit, short circuit, or short to ground in the left rear outlet valve solenoid coil inside the IPB hydraulic unit, causing drive current to exceed the calibrated threshold (typical abnormal range: 0.3-1.5A).
  • 2Brake fluid contamination (excessive water content, metal debris, or gelatinous deposits) causes the outlet valve spool to stick in the open or closed position, and the ECU detects abnormal position feedback.
  • 3IPB ECU internal valve body drive circuit fault, such as damaged MOSFET power transistor, burnt sampling resistor, or dry solder joint on the drive chip.
  • 4Water ingress, oxidation, or terminal back-out at the IPB wiring harness connector (32-pin or 48-pin main connector) causing excessive contact resistance in the valve body drive circuit.
  • 5Abnormal return fluid pressure shock from the left rear brake caliper or line causes mechanical damage to the valve body (common in vehicles with overdue brake fluid replacement).
What To Do
  • 1
    Use the BYD VDS2000 or diagnostic tool to access the IPB system. Read and confirm C001900 as a current fault (Active). Record the vehicle speed, hydraulic pressure, and valve body drive current values from the freeze frame data (Freeze Data).
  • 2
    Clear the fault code and perform the IPB dynamic function test: in a safe area, brake sharply at 20-40 km/h to trigger the ABS. Observe if the fault reoccurs; if it does, this confirms a hardware fault.
  • 3
    Disconnect the IPB assembly wiring harness connector and check the terminals for corrosion or water ingress (focus on the pin seals). Measure the resistance of the left rear outlet valve solenoid (standard value is typically 2-6 Ω, depending on the specific model). If the resistance is infinite or close to 0 Ω, this confirms valve body damage.
  • 4
    Check that the IPB power supply circuit (Terminal 30 constant power, Terminal 15 ignition switch) voltage is 12V ± 0.5V, the ground wire resistance is less than 1Ω, and the CAN-H and CAN-L line voltages are normal (approximately 2.5V).
  • 5
    If circuit measurements are normal but resistance is abnormal, or if the fault recurs shortly after clearing, replace the IPB integrated brake assembly (part numbers vary by model; e.g., 6A-3555100 series for Song PLUS DM-i). Do not replace the hydraulic valve body separately.
  • 6
    After replacement, perform the complete repair procedure: bleed the brake lines (use dedicated brake bleeding equipment or the traditional two-person bleeding method) → calibrate the steering angle sensor (G85) → calibrate the longitudinal acceleration sensor → calibrate the yaw rate sensor → perform a road test to verify ABS/ESP function
Real-World Cases
BYD DTC AI Analysis

BYD Seal 06 DM-i left rear outlet valve drive fault

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Vehicle: 2024 Seal 06 DM-i 120KM flagship variant, 8,500km. Symptoms: Dashboard intermittently displayed "Check ESP System", ABS and ESC warning lights illuminated, brake pedal felt normal. Diagnosis: Connected VDS2000 and scanned the IPB system. Retrieved current DTC C001900 (Left Rear Outlet Valve Drive Fault). Freeze frame showed vehicle speed was 35km/h when the fault occurred, with left rear outlet valve drive current at 0A (open circuit characteristic). Measured infinite resistance between Pin23 (Left Rear Outlet Valve +) and Pin24 (Left Rear Outlet Valve -) at IPB harness connector C07. Confirmed the hydraulic unit's internal solenoid coil had an open circuit. Repair: Replaced the IPB integrated brake assembly (Part No.: 6A-3555100-00). Performed brake bleeding and sensor calibration. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song PLUS DM-i Hydraulic Unit Valve Body Sticking

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Vehicle: 2021 Song PLUS DM-i 110KM Flagship PLUS, 42,000km. Symptoms: ESP warning light suddenly lit up during high-speed driving with "Check Brake System" alert; regenerative braking failed. Diagnosis: Scan tool pulled stored code C001900 from the IPB system plus C001800 (left rear inlet valve fault). Found complete failure of the left rear hydraulic valve assembly. Opened the IPB reservoir to find brake fluid dark brown (should be pale yellow) contaminated with metal debris. Root cause: Brake fluid never changed (over 40,000km), causing the valve spool to seize from lack of lubrication; high current draw burned out the ECU driver circuit. Repair: Replaced the IPB assembly, thoroughly flushed the brake lines, replaced all brake fluid with DOT4. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin Pro DM IPB hydraulic control unit fault

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Vehicle: 2019 BYD Qin Pro DM Super, 67,000 km. Symptoms: "Braking System Fault" warning on cold starts. Light cleared after driving but fault recurred. Diagnosis: DTCs C055F00 (Hydraulic Unit Abnormal) and intermittent C001900 stored. Found green corrosion inside 32-pin IPB harness connector (vehicle had been driven through water), causing intermittent open circuit in left rear outlet valve drive line. Cleaning the connector did not resolve. Valve body coil resistance measured 3.2Ω cold but drifted above 8Ω hot, confirming internal coil insulation degradation. Repair: Replaced IPB integrated braking unit and sealed wiring harness. Fault resolved.
Original source ↗
Other Seal U 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.