AU
B176D1B

DTC B176D1B indicates the front passenger Occupant Classification System (OCS) detects an abnormal signal or missing sensor — Seal U

Safety System

DTC B176D1B indicates the front passenger Occupant Classification System (OCS) detects an abnormal signal or missing sensor.

The system uses pressure/capacitive sensors integrated into the front passenger seat cushion to detect seat occupancy and weight category.

It transmits signals to the SRS airbag control unit to determine front passenger airbag deployment and deployment force during a collision.

This fault indicates the airbag control unit cannot receive a valid occupancy status signal (typically indicating an open circuit, out-of-range resistance, or signal plausibility error).

The system enters a fail-safe mode and defaults the front passenger seat status to "unoccupied".

This may prevent the front passenger airbag from deploying during a collision, severely compromising passive safety performance.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Repeated adjustment of the seat slide rail chafes and breaks the underlying wiring harness, specifically causing an open circuit in the power or signal wire.
  • 2Occupant sensor failure (internal open or short circuit). Defective sensor waterproofing commonly causes moisture damage.
  • 3Poor contact, oxidized pins, or a loose retaining clip at the yellow dedicated connector under the seat, causing intermittent signal interruption.
  • 4Failure to perform Occupant Detection System calibration after replacing the airbag control module or seat during accident repairs.
  • 5Poor connection or corrosion in the sensor power supply or ground circuit, causing abnormal voltage.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS2000/VDS2100) to read the fault code and view the data stream. Verify the 'Passenger Detection Sensor Status' displays 'Open Circuit', '255', or a fixed value that does not change with pressure.
  • 2
    Inspect the wiring harness routing under the front passenger seat, focusing on interference areas at the seat slide rail and frame. Open the corrugated conduit and check the wires for breaks or wear marks.
  • 3
    Disconnect the battery negative terminal and wait 3 minutes. Unplug the yellow connector under the seat. Check the pins for oxidation or backing out. Clean with electrical contact cleaner and apply conductive grease.
  • 4
    Measure the occupancy sensor resistance. Normal resistance varies with seat pressure between 200Ω and 1500Ω (standards vary slightly by model). If the resistance is infinite or fixed, replace the sensor assembly.
  • 5
    Check wiring harness continuity: Measure continuity of the wiring harness between the sensor connector and the Airbag Control Module (ACM), and check for short circuits to ground/power.
  • 6
    If replacing the seat or airbag control unit, perform the 'Passenger Detection System Zero Point Calibration': ensure the front passenger seat is completely empty (no items), then enter the SRS system special functions using the diagnostic tool to complete the calibration.
  • 7
    After repair, clear the fault code. Perform a static test (sit in and exit the front passenger seat and observe instrument cluster prompts) and a dynamic road test (drive over speed bumps to simulate vibration) to verify the fault is resolved.
Real-World Cases
BYD DTC AI Analysis

Song MAX seat track chafed through wiring harness causing open circuit.

✓
2019 Song MAX with constant airbag warning light on the instrument cluster. Scan tool showed DTC B176D1B. Found the seat runners under the front passenger seat chafing the wiring harness during fore-aft adjustment, completely severing the occupancy sensor power wire. Repair: Soldered the broken wire with double-layer heat-shrink insulation, rerouted and secured the harness above the seat frame to prevent interference. Cleared the DTC; the warning light went out and the system returned to normal. This is a known Song MAX issue caused by a wiring layout defect.
BYD DTC AI Analysis

Replaced failed sensor unit on Qin Pro DM

✓
2020 BYD Qin Pro DM. Airbag warning light illuminates within 10 seconds of startup. Front passenger seat belt reminder fails to trigger regardless of occupancy. Data stream shows 'passenger detection sensor status' stuck at open circuit (255). Removed sensor and measured infinite resistance, confirming internal open circuit. Replaced front passenger seat cushion assembly (integrated sensor and foam pad, part number SA-5820100). Performed OCS calibration with diagnostic tool; fault cleared. Suspect batch waterproofing defect allowed moisture ingress and failure.
BYD DTC AI Analysis

Tang DM-i connector pin oxidation, poor contact

✓
2021 Tang DM-i airbag warning light illuminates intermittently, occasionally extinguishing on rough roads and more frequent in humid weather. DTC B176D1B is intermittent. Inspection of the yellow connector under the seat revealed green oxide deposits inside; wiggling the connector caused the passenger airbag status in the data stream to toggle between Active and Fault. Fix: Disconnect the battery, clean the connector pins with electronic contact cleaner, apply conductive grease, and install wiring harness retaining clips to prevent loosening. Cleared the DTC and tested continuously over speed bumps with no recurrence. Common issue in humid southern regions.
BYD DTC AI Analysis

Song Pro system not calibrated after accident repair

✓
2018 BYD Song Pro showed DTC B176D1B after front-end accident repairs (front bumper and airbag control module replacement). Front passenger seat was occupied but the instrument cluster displayed the 'seat unoccupied' icon. Sensor hardware and wiring harness checked normal; 12V supply normal. Reviewed repair records and found OCS calibration was missed after the airbag control module replacement. Used VDS2000 to perform 'passenger detection system zero calibration', ensuring the seat was empty during the learning process. Subsequent occupant test showed normal instrument cluster indication. Common oversight in accident repair: a software configuration issue, not a hardware fault.
BYD DTC AI Analysis

Loose wiring harness connector on E2 EV caused signal interruption

✓
BYD E2 2019: Airbag warning light intermittently illuminates on rough roads; normal on flat surfaces. DTC B176D1B (intermittent). Inspection found the connector beneath the left rear seat (or passenger seat, depending on configuration) was not fully latched. Vehicle vibrations caused momentary signal interruption. Reconnected the plug ensuring the locking tab fully engaged, secured the wiring harness with cable ties to eliminate strain. Fault resolved. Common after frequent seat adjustment or seat removal.
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.