AU
B1620

DTC B1620 indicates the left Body Domain Controller detects an abnormal condition in the driver's side (left front) door lock — Qin Plus

Safety System

DTC B1620 indicates the left Body Domain Controller detects an abnormal condition in the driver's side (left front) door lock.

Specifically, the controller detects an implausible door lock position sensor signal, an open or short circuit in the door lock drive circuit, or a missing door lock status feedback signal.

Typical causes include faults in the door lock assembly microswitch, position sensor, actuator motor, or associated wiring harness connections.

This fault causes abnormal door status displays, remote locking failures, false anti-theft alarms, and false 'door open' warnings while driving, compromising vehicle security and driving safety.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Repeated bending of the wiring harness at the door hinge causes wear, insulation damage, or internal wire breakage (common issue on BYD models).
  • 2A faulty internal microswitch or position sensor in the front left door lock assembly causes abnormal signal voltage (normal: 0V/5V switching).
  • 3Loose wiring harness connector, poor contact, or oxidized pins causing signal interruption or excessive resistance.
  • 4Door lock motor internally burnt or coil open circuit (normal resistance approx. 2-3 Ω)
  • 5Improper wiring harness routing at the door waterproof membrane pinches the harness, causing a short to ground or a damaged signal wire.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to scan the left body domain controller, read and confirm DTC B1620, and verify the door lock status signal in the data stream matches the actual status.
  • 2
    Visually inspect the left front door lock wiring harness connector. Check for a loose plug, oxidized pins, or water ingress. Clean the connector or secure the retaining clip if necessary.
  • 3
    Inspect the wiring harness sleeve at the door hinge. Peel back the sleeve and inspect the internal wires for wear, damaged insulation, or breakage. Repair the wires and re-wrap the insulation.
  • 4
    Remove the left front door lock assembly. Measure the door lock motor resistance (standard value: 2-3 Ω) and check the motor for an open circuit. Measure the position sensor signal voltage and confirm the microswitch operating status.
  • 5
    If the wiring harness is damaged, repair the wiring harness. If internal door lock components are damaged, replace the left front door lock assembly (with sensor).
  • 6
    After reinstallation, use VDS to clear the fault code, perform door lock matching and learning (if required), and test the remote locking, mechanical key locking, interior switch locking, and anti-theft arming functions.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Left rear door lock fault causing false anti-theft alarm on the Seal

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Symptoms: The alarm triggered automatically after locking, the security system activated without cause, and the instrument cluster prompted to check the door lock system. Diagnosis: Scanned the left body domain controller using the VDS diagnostic tool and retrieved DTC B1C1200: Left Rear Door Lock Fault (current fault). Accessed live data from the left body domain controller to check the door lock status signal. Inspected the left rear door lock wiring harness connector and found poor contact. Measured the door lock motor resistance and position sensor signal, confirming the internal microswitch in the door lock was faulty. Resolution: Replaced the left rear door lock assembly. Re-secured the wiring harness connector for proper contact. Cleared the DTCs using VDS. Repeatedly tested the door lock switch and remote locking function. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Faulty left front door lock position signal caused false dashboard warnings in a Song Pro.

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Symptoms: Instrument cluster intermittently showed "Check door" message and abnormal door status. Vehicle indicated door open while driving. Diagnosis: Scanned body control system with VDS and found abnormal left front door lock position signal. Inspected left front door lock wiring loom – chafing at the door hinge. Measured door lock position sensor signal voltage and found it unstable (normal: switches between 0V and 5V). DTC indicated implausible door lock status signal. Resolution: Repaired chafed wiring and re-insulated the loom. Replaced left front door lock assembly (internal position sensor damaged). Re-adapted door lock parameters. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Tang DM left front door lock driver circuit fault causing lock failure

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**Symptoms:** After remotely locking the vehicle, the left front door failed to lock and the vehicle could not enter the anti-theft state. The instrument cluster displayed a message to check the door. **Diagnosis:** Used a diagnostic scan tool to retrieve fault codes from the left body domain controller, which indicated a left front door lock driver circuit fault. Inspected the left front door lock actuator and measured the motor resistance as open circuit (normal value approximately 2–3Ω). Checked the door lock fuse and power supply circuit, and confirmed the power supply was normal. Determined that internal burnout of the door lock motor caused the fault. **Resolution:** Replaced the left front door lock assembly. Inspected the door lock wiring harness connector and cleaned oxidised contacts. Tested remote locking, mechanical key locking, and interior switch locking functions—all functioned normally.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Abnormal right front door lock status signal on Song MAX caused automatic locking failure.

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Symptoms: While driving, the instrument cluster suddenly displayed "Check Door" and the automatic door locking function failed. Diagnosis: Scanned for DTCs using VDS. Found an abnormal right front door lock status signal (similar to B1620 door lock fault code). Live data showed the right front door switch status did not match the actual position. Removed the right front door trim panel and inspected the door lock wiring harness; the harness connector was loose. Reconnected the connector but the fault remained, indicating the internal micro switch in the door lock was faulty. Repair: Replaced the right front door lock actuator. Installed a retaining clip on the wiring harness connector to prevent it from working loose again. Cleared the fault codes and tested the door lock functions; fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro door lock wiring harness short circuit causes automatic unlocking after locking the vehicle

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After locking the vehicle, doors occasionally unlocked automatically and the instrument cluster displayed a door fault warning. Diagnosis: Diagnostic scan revealed left rear door lock DTCs (B1C series). Inspected the door lock wiring harness and found it crushed and damaged at the door waterproof membrane. Measured the door lock signal wire and found it shorted to ground, causing the control module to misinterpret the door status. Inspected the door lock actuator; motor operated normally, but found the position sensor signal wire damaged. Resolution: Repaired the damaged wiring harness and rerouted it to prevent crushing. Applied insulation and waterproofing to the damaged section. Cleared DTCs and performed an extended road test; fault did not recur.
Original source ↗
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself. Sources: [1]