AU
B2AB9-97

DTC B2AB9-97 indicates an internal fault or performance abnormality in the passenger seat Occupant Classification System (OCS) sensor, not "air conditioning load too high" as stated in the original information — Atto 8

Thermal Management System

DTC B2AB9-97 indicates an internal fault or performance abnormality in the passenger seat Occupant Classification System (OCS) sensor, not "air conditioning load too high" as stated in the original information.

Integrated into the front passenger seat cushion, the sensor uses pressure-sensitive elements to detect seat occupancy and passenger weight range.

It outputs an analogue voltage signal to the airbag control unit (SRS ECU) (normal range 2.5V-3.5V, varying with weight).

The ECU sets this code upon detecting a fixed sensor signal voltage, a voltage outside the valid range, or an open or short circuit exceeding the threshold.

This fault forcibly disables the front passenger airbag (the instrument cluster displays "PASS AIR BAG OFF") or prevents the system from adjusting the deployment strategy based on passenger weight during a collision.

This severely compromises passive safety system operation and requires immediate repair.

The B2AB9-97 fault code on the Atto 8 indicates a medium-severity internal fault or abnormal signal from the passenger seat Occupant Classification System sensor. This can disable the front passenger airbag or prevent correct airbag deployment adjustment. Common causes include a failed seat cushion OCS sensor or a loose, damaged, or intermittent under-seat wiring connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1OCS sensor faulty: Internal pressure-sensitive resistor or circuit board failure keeps the output signal voltage constant (e.g., stuck at 0.2V or 5V) and prevents it from changing with seat load.
  • 2Wiring harness connection fault: Loose connection at the dedicated yellow connector under the seat, backed-out terminal pins, broken locking tab, or wiring harness tension during seat track adjustment causing an intermittent open circuit.
  • 3Liquid ingress damage: Rainwater, beverages, or wet clothing penetrates the seat cushion, causing sensor circuit board oxidation, short circuits, or reduced insulation performance.
  • 4Software and calibration faults: SRS control unit software version mismatch, OTA update causing calibration data loss, or failure to complete the weight learning procedure after replacing the seat or sensor.
  • 5System configuration error: After replacing the seat assembly during accident repairs, the OCS sensor ID code stored in the SRS ECU does not match the new hardware, or the configuration parameters were not written.
What To Do
  • 1
    Diagnostic scan: Use BYD VDS or ED400 to access the SRS system, read the freeze frame data for DTC B2AB9-97, and check if the 'OCS sensor voltage' in the data stream varies with pressure within the 2.5V-3.5V range. If the voltage remains constant at 0V or 5V, it indicates an open or short circuit in the sensor or wiring.
  • 2
    Basic circuit inspection: Inspect the yellow 2-pin or 3-pin connector under the front passenger seat (usually located beneath the front of the seat) for looseness, water ingress, or corrosion. Measure the voltage from the connector power supply terminal to ground; it must be 12V (Ignition ON). Measure the resistance from the ground terminal to ground; it must be less than 1Ω.
  • 3
    Wiring harness dynamic test: Adjust the seat position forward and backward to check if the wiring harness interferes with the slide rail. Gently wiggle the wiring harness connector while monitoring the diagnostic tool data stream voltage for fluctuations to identify intermittent connections.
  • 4
    Sensor body inspection: Remove the front passenger seat cushion (remove the seat retaining bolts and flip the seat) and locate the OCS sensor integrated into the foam. Measure the sensor resistance. The normal range is approximately 1.5-3kΩ (refer to the workshop manual for specifics). If the resistance is infinite or zero, or if water stains or oxidation are visible, replace the sensor or seat cushion assembly.
  • 5
    Replacement and protection: After replacing the sensor, verify the seat foam is dry. If necessary, install a waterproof breathable membrane to prevent recurring water ingress. Install the new sensor and seat cushion in the correct positions, free from folds or compression.
  • 6
    System calibration: Use the diagnostic tool to perform 'OCS Zero Point Calibration' (unloaded state) and 'Weight Learning' (loaded state). Some models require manually entering the barcode ID on the sensor label or performing automatic configuration. After completing calibration, clear the fault code.
  • 7
    Function check: Test the following three conditions separately: empty seat; item under 5 kg on the seat (system must identify as child, airbag OFF); adult seated (system must identify as adult, airbag ON). Confirm correct instrument cluster indicator logic and verify the fault lamp turns off.
Real-World Cases
BYD DTC AI Analysis

BYD Qin Plus DM-i (2021) - Sensor unit damaged

✓
**Symptoms**: After starting the vehicle, the airbag warning light on the dashboard stays on. The passenger airbag displays "OFF" regardless of front passenger seat occupancy. **Diagnosis**: Connected VDS2000 and read the SRS data stream. The passenger-side OCS sensor output voltage remained constant at 0.2V (normal: varies between 2.5V–3.5V with pressure). Removed and inspected the yellow connector beneath the seat—no looseness or water ingress. Measured harness supply voltage (12V) and ground—both normal. Determined the sensor's internal pressure-sensitive element was damaged. **Solution**: Replaced the front passenger seat occupant sensor assembly (integrated in the seat cushion foam). Performed "OCS zero calibration" and "weight learning" after replacement (path: SRS system → Special functions → Seat occupant sensor calibration). Cleared fault codes after calibration. System returned to normal occupancy recognition.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro DM (2022) - Poor Contact in Wiring Harness Connector

✓
Symptoms: After interior cleaning, the airbag warning light came on intermittently and sometimes went out on bumpy roads. DTC B2AB9-97 was intermittent. Diagnosis: Inspected the wiring harness under the front passenger seat. Found the OCS sensor harness plug interfered with the seat rail during fore-aft adjustment. The plug locking clip was broken and the pins had poor contact. Tugging during cleaning worsened the contact. Voltage at the sensor plug dropped out when the harness was wiggled. Solution: Repaired the harness plug, replaced the damaged plug housing, re-crimped the harness terminals, and secured the harness to the seat frame with cable ties, routing it away from the rail. Cleared the DTC and tested with multiple seat adjustments; the fault did not recur.
Original source ↗
BYD DTC AI Analysis

BYD Han EV (2020) - Sensor damage from water ingress

✓
Symptoms: Airbag warning light illuminated after driving in heavy rain or through deep water. DTC B2AB9-97 stored. Front passenger seat had been covered with wet clothing for an extended period. Diagnosis: Removed and inspected front passenger seat. Found water stains at OCS sensor housing seal; internal circuit board oxidised. Liquid penetrated seat fabric into sensor, causing signal drift. Measured sensor resistance out of spec (normal ~1.5–3 kΩ). Fix: Replaced front passenger seat cushion assembly (OCS sensor and cushion are highly integrated; separate replacement cannot guarantee sealing). Checked seat foam for moisture and replaced damaged sections. Calibrated OCS system after installation. Added waterproof breathable membrane above sensor for extra protection.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM-p (2023 model) — Software program and calibration lost

✓
Symptoms: After OTA or multimedia system update, airbag warning light suddenly lit with DTC B2AB9-97. No accident or seat removal history. Diagnosis: Scanned with latest diagnostic tool. Found SRS control unit software version incompatible with OCS sensor hardware communication protocol, or seat occupant sensor calibration data lost during upgrade. Physical wiring and sensor appearance checked normal. Software logic error. Resolution: Reflashed SRS (airbag control unit) with latest software and performed complete OCS system configuration and calibration (zero-load and loaded). Some cases also require OCS sensor firmware upgrade. Cleared fault codes after programming. System normal.
Original source ↗
BYD DTC AI Analysis

BYD Seal (2022) - Configuration error after accident repair

✓
Symptoms: Front-end collision. After replacing the front bumper, airbags and other components, the airbag warning light came on at post-repair delivery. Retrieved DTC B2AB9-97: passenger airbag disabled. Diagnosis: Removed and reinstalled the passenger seat during collision repair. The sensor connector was secure, but the OCS sensor serial number or configuration parameters in the SRS control unit did not match the vehicle (possible causes: replacement seat assembly from a different batch, or incorrect data write to the control unit). The diagnostic tool displayed 'OCS not configured' or 'Configuration error'. Solution: Used the diagnostic tool to access the SRS system → Programming/Configuration, and rewrote the correct OCS sensor ID code (manually input the barcode from the sensor label or performed automatic recognition). After completing the configuration, ran the 'System Learn' or 'Calibration' procedure so the control unit recognizes the new sensor. Cleared the fault codes; the airbag warning light went out and the collision recovery system returned to normal.
Original source ↗
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.