AU
B17261A

DTC B17261A indicates the front passenger seat Occupant Classification System (OCS) sensor detects a circuit resistance of 0 or an open circuit — Atto 8

Safety System

DTC B17261A indicates the front passenger seat Occupant Classification System (OCS) sensor detects a circuit resistance of 0 or an open circuit.

This sensor integrates into the front passenger seat cushion and uses pressure-sensing elements to monitor seat occupancy status in real time (empty/child/adult classification).

A resistance of 0 typically indicates a short to ground in the sensor power or signal wire, an internal open circuit, or a disconnected connector.

This fault causes the airbag control unit (SDM) to enter degraded mode, preventing it from accurately determining the front passenger type during a collision.

The SDM may incorrectly suppress the front passenger frontal and knee airbags, or cause unintended airbag deployment, severely compromising the passive safety system protection strategy.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Ruptured pressure-sensing diaphragm inside the OCS sensor body or burnt circuit board causing abnormal resistance (normal range: 50-200 Ω).
  • 2Loose, oxidized, backed-out pins, or poor contact at the white 4-6 pin wiring harness connector under the seat, causing signal interruption.
  • 3Excessive pulling of the seat wiring harness during vehicle modifications (such as fitting leather upholstery or installing seat cushions) or repairs, causing internal wire breakage.
  • 4A loose or misaligned sensor mounting bracket causes abnormal stress between the sensor and the seat frame, breaking the internal circuit.
  • 5Vehicle wading or liquid ingress into the seat interior causes the sensor connector to short circuit and melt, resulting in an open circuit.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool VDS to read the fault codes, confirm the B17261A current status and freeze frame data, and check for related fault codes such as 'Lost communication with front passenger seat occupancy sensor'.
  • 2
    Visually inspect the OCS sensor wiring harness connector under the front passenger seat (usually located in front of the seat slide rail) for looseness, backed-out pins, or oxidation, and check the wiring harness for pinching or damage.
  • 3
    Disconnect the battery negative terminal and remove the front passenger seat. Use a multimeter to measure the OCS sensor resistance (standard value: 50-200 Ω; a reading of 0 or infinity indicates a fault). Also measure harness continuity and insulation resistance to ground.
  • 4
    If plug contact is poor: Clean the pins with electrical contact cleaner, repair backed-out terminals, apply conductive grease to improve contact, reconnect the plug, and secure it to the seat frame with cable ties to prevent loosening.
  • 5
    If the wiring harness is broken: strip the harness insulation, locate the break, solder the repair, and apply waterproof insulating tape; if the sensor body is damaged, replace the OCS sensor assembly (some models require replacing the entire seat cushion foam assembly).
  • 6
    After reinstalling the seat, connect the diagnostic tool and execute the OCS system calibration procedure. Following the workshop manual, sequentially place 0kg, 6kg, and 36kg (or 30kg to simulate an adult) standard weights for multi-point calibration. Verify the SDM correctly identifies the resistance values for each state.
  • 7
    Clear the fault code and perform a road test to verify the airbag warning light turns off and the OCS status in the data stream switches normally with changes in passenger weight.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM front passenger OCS sensor internal fault

✓
Symptoms: Dashboard airbag warning light on, multimedia screen displaying 'Please check airbag system'. Restarting did not clear the warning. Diagnosis: VDS read DTC B17261A. Removed and inspected the seat, measured infinite resistance (open circuit) at the OCS sensor, confirming damage to the internal pressure sensing element. Solution: Replaced the front passenger seat OCS sensor assembly. Performed OCS system calibration using VDS (calibrated with a standard weight), cleared the fault codes and resolved the issue.
Original source ↗
BYD DTC AI Analysis

BYD Han EV: Poor contact at seat wiring harness connector

✓
Symptoms: Airbag warning light illuminates intermittently, often triggered by adjusting the front passenger seat position or driving over rough surfaces; occasionally extinguishes after restarting. Diagnosis: Retrieved DTC B17261A (intermittent). Inspection found the OCS connector beneath the seat loose, with oxidized and backed-out pins; measurement indicated intermittent contact resistance. Solution: Cleaned the connector pins, repaired the backed-out terminals, applied conductive grease, reconnected firmly, and secured with a cable tie. Monitored for one week with no recurrence.
Original source ↗
BYD DTC AI Analysis

Sensor quality issue on new BYD Song Plus DM-i

✓
Symptoms: The dashboard suddenly displayed an airbag fault after the vehicle had been driven 1000–3000 km; no collision or modification history. Diagnosis: The dealership found DTC B17261A, confirming an OCS sensor manufacturing defect or pressure damage during transport. The wiring harness connections were normal with no water ingress. Resolution: Replaced the front passenger seat OCS sensor assembly under warranty, updated the SDM software to the latest version to optimise signal recognition, and calibrated the system, which resolved the fault.
Original source ↗
BYD DTC AI Analysis

Wiring harness damaged after removing and installing seat on BYD Qin Plus DM-i

✓
Symptoms: Airbag warning light illuminates after leather upholstery or interior trim modification. Some cases occurred after window tinting at dealerships. Diagnosis: Retrieved DTC B17261A and 'Lost communication with OCS' history codes. Found excessive pulling on the wiring harness during modification fractured internal wires or damaged connector clips. Solution: Repaired the fractured wiring harness, replaced damaged connectors, ensured correct installation of the OCS sensor mounting bracket, and recalibrated the OCS system.
Original source ↗
Other Atto 8 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.