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 — Atto 8

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).

The C001900 fault code on the Atto 8 indicates a medium-severity problem with the rear left outlet valve in the IPB brake hydraulic unit. It can be caused by an open or short circuit in the valve solenoid, or by brake fluid contamination causing the valve to stick. ABS, ESC, regenerative braking, and emergency braking may be limited. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Open circuit, short circuit, or short to ground in the left rear outlet valve solenoid coil inside the IPB hydraulic unit causes drive current to exceed the calibrated threshold (typical abnormal range: 0.3-1.5A).
  • 2Brake fluid contamination (excessive water content, metal debris, or gel-like deposits) causes the outlet valve spool to stick in the open or closed position, causing the ECU to detect abnormal position feedback.
  • 3IPB ECU internal valve body drive circuit fault, such as a damaged power MOSFET, a burnt sampling resistor, or a poor solder joint on the driver 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 surge from the left rear brake caliper or lines causes mechanical damage to the valve body (common in vehicles lacking regular brake fluid replacement).
What To Do
  • 1
    Use the BYD VDS2000 or a diagnostic tool to access the IPB system, read and confirm C001900 is a current fault (Active), and record the vehicle speed, hydraulic pressure, and valve body drive current values from the freeze frame data (Freeze Data).
  • 2
    Clear the fault codes and perform the IPB dynamic function test: in a safe area, drive at 20-40 km/h and brake sharply to trigger ABS operation. Observe whether the fault recurs. If the fault recurs, confirm a hardware fault.
  • 3
    Disconnect the IPB assembly wiring harness connector. Inspect the terminals for corrosion or water ingress (focus on the pin seals). Measure the left rear outlet valve solenoid resistance (standard value is typically 2-6 Ω, depending on the specific model). If the resistance is infinite or close to 0 Ω, the valve body is damaged.
  • 4
    Check that the IPB power supply circuit voltages (constant power Terminal 30, ignition switch Terminal 15) are 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 returns soon after clearing, replace the IPB integrated brake assembly (part numbers vary by vehicle 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 brake lines (using dedicated brake bleeding equipment or traditional two-person method) → calibrate steering angle sensor (G85) → calibrate longitudinal acceleration sensor → calibrate yaw rate sensor → 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 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.