AU
B2AB573

This DTC indicates an abnormal driver seat fore-aft position sensor signal or a Seat Control Unit (SCU) communication fault — Atto 3

Thermal Management System

This DTC indicates an abnormal driver seat fore-aft position sensor signal or a Seat Control Unit (SCU) communication fault.

The ECU detects a sensor signal voltage outside the normal range (0.5-4.5V), an inconsistent signal, or a complete signal loss.

This disables the seat memory system and easy entry/exit functions.

Typically a Hall-effect or potentiometer type, the sensor mounts on the seat rail.

It monitors the seat fore-aft position in real time, providing position feedback to the memory function and intelligent cockpit system.

Although the fault message displays "start-up failure", a seat position signal failure actually prevents the related functions from starting.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Oxidized, loose, or corroded pins (green corrosion) at the under-seat wiring harness connector, causing interrupted signal transmission or excessive resistance.
  • 2Faulty longitudinal position sensor (internal wiper wear, Hall element failure, or resistor open circuit), causing the signal to jump or remain fixed at a specific position.
  • 3Jammed seat rail, foreign object ingress (such as coins), or insufficient lubrication, causing excessive wear of the sensor mechanical structure, stalling, or motor overload.
  • 4Damaged Seat Control Unit (SCU) internal driver chip or abnormal supply voltage (battery voltage below 11.5V causing signal distortion)
  • 5Intermittent connection caused by stretching the wiring harness, breaking the connector latch, or failing to fully engage the connector during vehicle modifications (such as installing seat ventilation/heating pads).
What To Do
  • 1
    Use VDS2000 or Launch X431 to read the Seat Control Unit (SCU) fault codes, confirm B2AB573 is a current code, and check the freeze frame data for the seat status recorded when the fault occurred.
  • 2
    Access the data stream and monitor the "driver seat fore-aft position" value. Manually move the seat through its full travel range and observe if the value changes linearly (the value should change continuously between 0-255mm or 0.5-4.5V, without jumps or fixed values).
  • 3
    Inspect the under-seat wiring harness connector (usually located at the front or side of the seat rail) for oxidation, green corrosion, loose connections, or pin corrosion. If necessary, clean the connector and apply conductive grease.
  • 4
    Disconnect the sensor connector, measure the supply voltage (5V reference) and verify the ground; measure the sensor resistance (potentiometer type: normally 2-3kΩ, changing continuously as the seat moves) or signal voltage (Hall type).
  • 5
    Check the seat rails for foreign objects, deformation, or insufficient lubrication. Clean the rails and apply the specified grease. Ensure the seat moves smoothly without binding.
  • 6
    If the sensor is damaged, replace the driver seat fore-aft position sensor (on some models, the sensor is integrated with the seat frame, requiring partial seat disassembly).
  • 7
    If the wiring harness or connector is damaged, repair the wiring harness, replace damaged connector retaining clips, and secure the connection with cable ties to prevent poor contact.
  • 8
    Perform seat memory system calibration: Use the diagnostic tool to enter Special Functions → Seat Memory Calibration. Follow the prompts to move the seat to the foremost and rearmost limit positions to complete self-learning, and save the position data.
  • 9
    Clear the fault code and test the seat memory 1/2/3 position storage and recall, easy entry/exit function (moves back at power off/restores at start-up), and reverse-linked exterior mirror function for normal operation.
Real-World Cases
BYD DTC AI Analysis

Tang DM-i seat memory function completely failed

✓
Symptoms: Instrument cluster displayed "Please check seat system". Memory and easy entry/exit failed completely. Manual adjustment worked, but the system would not save positions. Diagnosis: SCU showed code B2AB573. Data stream showed longitudinal position fixed at 255 cm. Removed and inspected the sensor harness connector; found oxidation with green corrosion on the pins. Sensor measured open circuit. Solution: Cleaned the harness connector and applied conductive grease. Replaced the driver seat longitudinal position sensor. Performed seat memory system calibration (moved seat to full forward and rearward positions to complete learning). Cleared fault codes; functions restored.
BYD DTC AI Analysis

Han EV: Abnormal Seat Sliding / Seat Position Memory Malfunction

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Symptoms: After sitting overnight, the seat automatically moved forward against the steering wheel on startup. Saved memory positions recalled with 10–15cm deviation. Fault occasionally reported while driving. Diagnosis: Retrieved DTC B2AB573 (Range/Performance) accompanied by U01B487 (Communication). Found a foreign object (coin) jamming the rails. After clearing it, live data showed the position jumping from 20cm to 80cm. Determined the sensor’s internal slider had poor contact. Battery voltage also measured low at 11.2V. Solution: Replaced the driver seat longitudinal position sensor assembly and seat control module (SCU—as the stall condition likely overloaded the driver chip). Completed seat memory initialization and calibration. Recommend checking battery state of health.
BYD DTC AI Analysis

BYD Song PLUS DM-i Easy Entry/Exit function inoperative

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Symptoms: When shutting down and opening the door, the seat does not automatically move rearward (Easy Entry failed). Reverse mirror tilt functions normally. Manual adjustment occasionally stutters or jumps; the system will not save new memory positions. Diagnosis: Retrieved DTC B2AB573 (present in history and current). Freeze frame data showed the seat moving rearward when the fault occurred, with the signal suddenly dropping out. On-vehicle testing revealed the sensor value dropped to "0" (signal loss) when the seat reached a specific position (mid-to-rear). Resolution: Replaced the seat longitudinal position sensor (individual sensor, not the complete assembly). Checked the runner lubrication and applied grease. Reset the seat memory positions. Tested the Easy Entry function—now operating normally.
BYD DTC AI Analysis

Seal seat memory malfunction / simultaneous fault codes across multiple systems

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Symptoms: 3-month-old vehicle. Intermittent seat memory failure with inoperative lumbar support adjustment. During faults, fore-aft seat adjustment slowed and memory buttons were unresponsive. Diagnosis: SCU scan revealed DTCs B2AB573 (longitudinal position sensor) and B2AB673 (height position sensor) plus additional sensor faults. Inspection found the owner had disturbed the wiring harness while installing aftermarket seat ventilation/heating pads. The longitudinal position sensor connector was not fully seated due to a broken locking clip, causing poor contact; technicians measured high resistance on the signal line. Resolution: Re-secured the wiring harness connector and used cable ties to ensure reliable connection. Replaced the damaged connector locking clip. Cleared all DTCs and performed a full seat travel initialisation procedure. Cautioned the owner to protect the factory wiring harness during future modifications.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.