AU
B165800

This DTC indicates a communication link fault between the SRS (Supplemental Restraint System) control unit and the Left Front Impact Sensor (LFIS) — Seal U

Safety System

This DTC indicates a communication link fault between the SRS (Supplemental Restraint System) control unit and the Left Front Impact Sensor (LFIS).

This typically indicates an interrupted LIN bus or private CAN communication between the sensor and the Airbag Control Module (ACM), a data validation failure, or a signal timeout.

The LFIS monitors deceleration changes in the vehicle's left front area and provides the SRS control unit with critical collision severity data to determine whether to deploy the driver airbag, left curtain airbag, and seatbelt pretensioner.

This communication fault prevents the control unit from receiving collision information for this zone.

Consequently, it may cause unintended airbag deployment (fail-safe mode) or delay or prevent the activation of left-side protection devices during an actual collision.

This constitutes a critical fault in the active safety system.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Water ingress, oxidation, or backed-out pins in the left front crash sensor wiring harness connector: The sensor mounts near the left front longitudinal beam or bumper bracket. Poor connector sealing allows water entry during wading, car washing, or driving in the rain, which corrodes the terminals and increases contact resistance.
  • 2Sensor power supply or ground circuit fault: includes blown fuse, or wiring open/short circuit (especially after front-end accident repairs where an improperly secured wiring harness rubs against metal body edges, damaging the insulation).
  • 3Left front crash sensor internal fault: Internal accelerometer or communication chip damage prevents response to the SRS control unit handshake signal.
  • 4SRS control unit (airbag control module) internal communication port fault: The control unit circuit module receiving the signal for this specific channel is damaged.
  • 5Harness shield failure or electromagnetic interference: Damage to the front compartment harness shield causes high-frequency interference, resulting in communication data packet checksum failure.
What To Do
  • 1
    Use a BYD VDS2000 or Launch X431 diagnostic tool to access the SRS system. Read all fault codes and record the freeze frame data. Confirm whether B165800 is a current (Present) or historical (History) fault, and check for related fault codes (such as B165700 parameter error).
  • 2
    Disconnect the battery negative terminal and wait 3 minutes to fully discharge the SRS capacitor to ensure safety. Locate the left front crash sensor (usually mounted on the front section of the left front longitudinal beam or behind the headlamp bracket) and check the sensor housing for physical damage, cracks, or signs of water ingress.
  • 3
    Disconnect the sensor connector and check the terminals for oxidation, backed-out pins, or spreading. Clean the terminals with electronic contact cleaner and apply conductive protective compound. Measure the resistance between the sensor-side terminals to confirm no internal short circuit exists (standard value is usually infinite or the manufacturer’s specified value).
  • 4
    Reconnect the connector, turn the ignition switch to ON (do not start), and use a multimeter to measure the sensor supply voltage (should be 9-16 V, depending on the vehicle model), ground resistance (should be less than 1 Ω), and LIN line voltage (typically a 7-11 V pulse voltage, average value about 9 V).
  • 5
    If the voltage is abnormal, disconnect the SRS control unit connector. Use an oscilloscope to check the LIN bus waveform and confirm the control unit sends the correct wake-up signal (typically a 12V high level or a square wave at a specific frequency). Measure the wiring harness continuity, specifically inspecting the harness fixing point at the front left longitudinal beam in the front compartment for wear.
  • 6
    If wiring harness measurements are normal, perform a sensor substitution test: install a known good left front crash sensor, clear the fault code, perform an ignition cycle test, and use the diagnostic tool to run the 'Crash Sensor Calibration' procedure (some models require a dedicated calibration tool).
  • 7
    If the fault remains after replacing the sensor, check the SRS control unit software version and upgrade it if necessary. If the software is normal, this indicates an internal fault in the SRS control unit. Replace the control unit and reconfigure the vehicle VIN and sensor parameters.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Left front crash sensor communication lost after water ingress

✓
A 2019 BYD Qin Pro DM had an airbag warning light that stayed on after driving in heavy rain. The system stored DTC B165800. Inspection found obvious water staining inside the collision sensor connector below the left front longitudinal beam, with green corrosion on the terminals. The front bumper undertray had cracked during a previous underbody scrape, allowing water to be forced into the sensor connector when driving through standing water. Repair involved thoroughly cleaning the connector with precision electronic cleaner, replacing the waterproof seal, and applying waterproof insulating tape to the connector. After clearing the fault code and performing three ignition cycle tests, the fault did not recur.
BYD DTC AI AnalysisFrom Chinese market (translated)

After accident repair, a loose wiring harness connection caused an intermittent communication fault.

✓
2018 Qin Pro petrol variant. After a minor collision on the left front, the dealership replaced the left front fender and bumper. One week later, the airbag warning lamp illuminated intermittently, and the diagnostic tool displayed intermittent fault code B165800. Inspection found that during the repair, the left front impact sensor wiring harness connector had not been fully locked — its retaining clip was only partially engaged, causing intermittent contact as the vehicle moved. Fix: Re-routed and secured the wiring harness, made sure the connector clip clicked fully into place, then used cable ties to fix the harness to the longitudinal beam bracket to stop movement. After a month of monitoring, the fault has not recurred.
BYD DTC AI AnalysisFrom Chinese market (translated)

Hard fault due to sensor body damage.

✓
2019 BYD Qin Pro DM. Airbag warning light stays on continuously. DTC B165800 present and could not be cleared. Checked sensor power supply (12.4V) and ground (0.3Ω) — both normal. LIN line voltage measured 0V with ignition ON (should normally read approx 9V pulse). Diagnosed internal short in sensor pulling bus low. Removed sensor and found fine cracks on its housing, likely from stress during a previous bottoming-out impact. Replaced with a new left front impact sensor. Used VDS2000 to perform SRS system configuration and impact sensor zero calibration. Fault resolved. System returned to normal self-check status.
BYD DTC AI AnalysisFrom Chinese market (translated)

False positive caused by software calibration error

✓
A 2018 BYD Qin Pro displayed DTC B165800 after a battery replacement. The vehicle had no collision history, and the wiring harness measured normal. Diagnosis found the battery was disconnected too long during the swap, causing the SRS control unit to lose sensor calibration data stored in non-volatile memory. Fix: Use the BYD dedicated diagnostic tool to enter SRS special functions, then run "Sensor ID Registration" and "Longitudinal/Lateral Acceleration Zero-Point Calibration." Clear the DTC after completing both—the airbag warning light goes out. This fault tends to occur when the battery is disconnected for more than 30 minutes. It's a software configuration issue, not a hardware failure.
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. Sources: [1]