AU
B1654

DTC B1654 indicates the SRS (Supplemental Restraint System) ECU detected a communication interruption or abnormal circuit impedance between the Left Front Impact Sensor and the main controller during self-check or operation — Seal U

Safety System

DTC B1654 indicates the SRS (Supplemental Restraint System) ECU detected a communication interruption or abnormal circuit impedance between the Left Front Impact Sensor and the main controller during self-check or operation.

This sensor typically mounts to the left front longitudinal beam, headlamp bracket, or fender reinforcement beam to monitor collision acceleration on the left front side of the vehicle.

The ECU sets this DTC if it fails to receive a valid signal from the sensor within a predetermined time, or if it detects an open or short circuit in the wiring.

Under this condition, the airbag system enters fail-safe mode, potentially disabling the left front collision detection function.

This compromises the deployment logic of the airbags and seatbelt pretensioners during a frontal collision, posing a major safety risk.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Sensor harness open circuit or short circuit: improperly secured harness after front-end collision repairs; harness damage caused by vibration and friction during long-term use; or circuit interruption from rodents gnawing the wiring.
  • 2Poor connector contact: Left front crash sensor plug is loose, pins are backed out, oxidized, or corroded (common in vehicles driven through water or after high-pressure washing), interrupting signal transmission.
  • 3Sensor fault: A damaged internal piezoelectric or capacitive accelerometer element, or an open internal diagnostic resistor, prevents the sensor from returning the correct bias voltage or PWM signal to the SRS ECU.
  • 4Abnormal installation position: After accident repairs, failure to install the sensor to the standard torque (usually 8-10 N·m) or installing it in the wrong orientation triggers the internal open-circuit protection mechanism.
  • 5SRS ECU internal fault: Damaged internal sampling circuit, A/D converter, or pull-up resistor for the left front crash sensor (relatively rare; rule out wiring faults before confirming)
What To Do
  • 1
    Diagnostic confirmation: Use VDS2000 or a dedicated BYD diagnostic tool to read the fault code and determine if B1654 is an Active or History fault. For History faults, check the trigger conditions (vehicle speed, timestamp) in the freeze frame data.
  • 2
    Visual inspection: Open the front compartment and locate the left front crash sensor (typically at the front end of the left front longitudinal beam, with a yellow connector). Check the sensor for physical damage or cracks, inspect the mounting bracket for deformation, and check the mounting torque mark for misalignment.
  • 3
    Connector inspection: Disconnect the 12 V battery negative terminal. Wait at least 90 seconds for capacitor discharge, then unplug the sensor connector. Check the connector pins (usually 2-3 pins) for oxidation, burn marks, or backed-out pins. Check the harness-side connector for signs of water ingress. Clean the contacts with electrical contact cleaner and apply conductive grease.
  • 4
    Circuit continuity test: Use a multimeter to measure sensor wiring harness continuity from the connector to the SRS ECU (typically a twisted pair, yellow/black or yellow/blue). Normal resistance must be less than 1 Ω. Measure insulation resistance to ground and power; it must be greater than 10 MΩ. If the circuit is open, remove the corrugated conduit and repair the wiring harness.
  • 5
    Sensor body test: If wiring is normal, measure sensor body resistance (refer to the workshop manual; typically 2.0-3.0 kΩ depending on the specific model). If resistance is infinite or zero, replace the sensor. Note: Some models require genuine parts. Sensor resistance characteristics may vary between batches.
  • 6
    System reset and verification: Reconnect all connectors and the battery. Use the diagnostic tool to clear the fault code, then perform a 'Sensor Check' or 'System Self-Test'. Observe the data stream to verify the 'Left Front Impact Sensor' status displays 'Normal' or the correct voltage value (typically around 2.5V bias voltage). Perform an ignition cycle test (ON-OFF-ON) to confirm the fault code does not reappear.
  • 7
    Collision simulation test (if necessary): Ensure safe conditions, then use the diagnostic tool to execute the 'Collision Sensor Test' function, or lightly tap the vehicle body near the sensor (do not tap the sensor directly). Observe the acceleration value changes in the data stream to confirm normal sensor dynamic response.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Wiring harness not plugged in after accident repair caused B1654.

✓
Model: BYD Tang DM 2021. Symptom: After repairs following a minor front-end collision, the airbag warning light on the instrument panel stayed on. Diagnosis: Retrieved DTC B1654 (active fault). Inspection revealed that after panel beating repairs to the left front rail, the technician failed to reconnect the left front impact sensor harness connector, leaving the wiring harness dangling inside the fender liner. Resolution: Reconnected the sensor connector, applied conductive paste, and secured the harness with cable ties to prevent chafing against the bodywork. Cleared the fault code and the system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Corroded sensor connector on water-damaged vehicle

✓
Vehicle: BYD Yuan EV 2019. Symptom: Airbag warning light illuminated after driving through floodwater during heavy rain. Diagnosis: VDS scan reported DTC B1654. Removed the left front impact sensor and found obvious water ingress inside the connector. The pins showed green copper corrosion, causing increased contact resistance on the signal line (measured 15 Ω; normal < 1 Ω). Solution: Replaced the wiring harness connector (cut and splice), cleaned and polished the sensor pins, and applied silicone grease to the connector seal to improve waterproofing. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Rodents chewed through the wiring, causing an intermittent fault.

✓
Vehicle: 2019 BYD Song MAX. Symptoms: SRS warning light illuminates intermittently, particularly on rough roads. Diagnosis: DTC B1654: intermittent historical fault. Inspected the left front impact sensor wiring harness and found rodent damage inside the corrugated tubing. The signal wire conductor had partially fractured, with only a few copper strands maintaining the connection. Vehicle vibration caused the circuit to open, triggering the fault. Repair: Repaired the harness by soldering the broken conductor and sealing it with heat-shrink tubing. Installed rodent mesh and rerouted the harness away from rodent-prone areas. This completely resolved the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal open circuit in sensor body

✓
Vehicle: 2020 BYD Qin Pro (petrol). Symptom: Airbag warning light suddenly illuminated; no accident history. Diagnosis: DTC B1654 active. Measured sensor harness continuity and insulation – both normal. Connector voltage normal (12V or 5V reference). Removed sensor and measured infinite resistance (spec: approx. 2.5 kΩ). Repair: Replaced the OEM left front impact sensor (part number must match vehicle VIN). Torqued mounting bolt to 9 N·m. Performed system configuration (some models require sensor ID programming via diagnostic tool). Fault cleared.
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]