AU
B1676

DTC B1676 indicates the airbag control unit (SRS ECU) detected a communication loss or physical disconnection at the Left Rear Side Impact Sensor — Seal U

Safety System

DTC B1676 indicates the airbag control unit (SRS ECU) detected a communication loss or physical disconnection at the Left Rear Side Impact Sensor.

Located in the left rear C-pillar or rear door frame area, this sensor monitors collision acceleration at the left rear of the vehicle.

The SRS ECU stores this DTC if it fails to receive a sensor signal within a predetermined time or detects abnormal circuit resistance (open/short circuit).

This fault forces the side airbag system (including the side curtain and/or rear seat side airbags) into a degraded mode.

The airbags may fail to deploy during a left-side collision, severely compromising passive safety.

Repair immediately.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose sensor connector, backed-out pins, or oxidized/corroded terminals inside the left rear C-pillar trim panel (common after vehicle wading, high-pressure washing, or prolonged exposure to damp conditions)
  • 2Broken internal wires in the sensor wiring harness due to long-term bending and wear at the door hinge or C-pillar sheet metal hole.
  • 3Internal accelerometer failure in the side impact sensor (e.g., previous side impact without airbag deployment, or sensor failure due to aging)
  • 4Communication lines (usually twisted pair) between the SRS control unit and the sensor shorted to ground, shorted to power, or shorted to each other.
  • 5Loose, deformed, or detached sensor mounting bracket causing poor connector contact or sensor failure.
What To Do
  • 1
    Safety preparation: Turn off the ignition, disconnect the 12V battery negative terminal, and wait at least 90 seconds for the SRS system energy storage capacitor to fully discharge to prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the left rear C-pillar trim panel and sill trim panel. Locate the side impact sensor (usually marked 'SIDE IMPACT' or with a part number). Verify the connector is fully seated and check for a broken retaining clip. Inspect the pins for green oxidation, corrosion, or backed-out terminals.
  • 3
    Wiring continuity check: Disconnect the sensor connector and the SRS ECU connector. Use a multimeter to measure the wiring harness continuity between them. Normal resistance must be less than 1 Ω. Measure the circuit insulation to ground and to power. The resistance must be greater than 1 MΩ to rule out a short circuit.
  • 4
    Sensor body inspection: If the wiring harness is normal, measure the sensor body resistance (refer to the BYD workshop manual; typically 2-3 kΩ depending on model year). Lightly tap the sensor housing and observe for sudden resistance changes. Replace the sensor if abnormal.
  • 5
    System Reset and Verification: After repairing the wiring harness or replacing the sensor, reconnect all connectors and the battery. Use the VDS2000/VDS3000 diagnostic tool to clear the fault code. Perform the 'SRS System Self-Diagnosis' and 'Configuration and Calibration' procedures. Confirm B1676 does not return and the system status is 'Normal'.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Water ingress caused oxidation of the left rear C-pillar connector, resulting in intermittent warnings.

✓
Vehicle: 2019 BYD Song MAX. Symptom: Airbag warning light illuminates intermittently while driving, with frequency significantly increasing during rainy or humid conditions. Scan tool retrieved active fault code B1676. Repair procedure: Removed the left rear C-pillar trim panel and found obvious water stains and green copper oxide inside the side impact sensor connector. Traced the leak to a perished upper C-pillar seal allowing rainwater ingress. Rectification: Cleaned the connector pins using electronic contact cleaner, applied conductive protective silicone grease, replaced the C-pillar seal, and re-secured the wiring harness waterproof boot. Cleared the fault code and monitored for one week with no recurrence.
BYD DTC AI AnalysisFrom Chinese market (translated)

Wiring harness crushed after accident repair

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Vehicle symptoms: 2021 BYD Tang. After a minor scrape on the left rear side, repaired at a non-authorised shop (panel beating and spray painting), the airbag warning light remained on after delivery. VDS diagnosis showed B1676. Repair process: Checked the wiring harness routing in the left rear door frame. Found that during the accident repair, the shop had not reinstalled the harness securing clips. When closing the door, the sharp edge of the C-pillar pinched the harness, breaking the communication wire internally while the outer insulation looked intact. Resolution: Repaired the harness by soldering and heat-shrink insulation. Rerouted the harness and added anti-chafing corrugated tubing. Ensured the harness has enough slack during door operation and does not contact panel edges.
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket window tint installation caused the connector to come loose.

✓
Vehicle Symptoms: 2019 BYD Yuan EV. Airbag warning light illuminated after window film installation. Diagnostic check revealed current fault code B1676. Repair Process: Owner reported the left rear C‑pillar interior trim had been removed during the film work. Inspection of the sensor connector showed the plug was not fully seated, relying only on slight pin contact. Driving vibration caused excessive contact resistance, triggering the fault code. Resolution: Re‑seated the connector until it clicked into place, secured the wiring harness with a cable tie to prevent loosening, and cleared the fault codes. System returned to normal operation. Recommendation: Advised owner to select a reputable tinting workshop with airbag system knowledge for future work.
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]