AU
B176D1B

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

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.

The B176D1B fault code on the Qin Plus indicates an abnormal or missing signal from the front passenger Occupant Classification System. Severity is medium because the system may default the passenger seat to unoccupied, which can prevent airbag deployment in a crash. Common causes include worn or broken seat wiring from seat movement, or a failed moisture-damaged occupant sensor. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Repeated seat track adjustment wears and breaks the underlying wiring harness, specifically causing open circuits in the power or signal wires.
  • 2Occupant sensor unit 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.
  • 5Loose connection or corrosion in the sensor power supply circuit 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 if the 'Passenger Detection Sensor Status' displays 'Open Circuit', '255', or a fixed value that does not change with pressure.
  • 2
    Check the wiring harness routing under the front passenger seat, focusing on the interference area between the seat slide rail and frame. Open the corrugated conduit and inspect 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 the pins 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 remains fixed, replace the sensor assembly.
  • 5
    Check wiring harness continuity: Measure wiring harness continuity between the sensor connector and the airbag control module (ACM), and check for shorts to ground or power.
  • 6
    If replacing the seat or airbag control unit, perform the 'Passenger Detection System Zero-Point Calibration': Verify the front passenger seat is completely empty (no items), then access the SRS system special functions via 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 the 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 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus overview →
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.