AU
B161B1A

DTC B161B1A indicates the airbag control module (SRS ECU) detects the Passenger Front Airbag ignition circuit resistance is below the calibrated threshold (typically below 1 — Seal U

Safety System

DTC B161B1A indicates the airbag control module (SRS ECU) detects the Passenger Front Airbag ignition circuit resistance is below the calibrated threshold (typically below 1.0-1.5Ω; normal range is generally 2.0-5.0Ω).

Low resistance typically indicates a parallel short circuit path in the airbag circuit.

Potential causes include a wiring harness short to ground, bridged connector pins, or an internal short circuit in the airbag inflator.

The ECU classifies this as a "Low Resistance" fault.

This condition can prevent proper airbag deployment during a collision because the short circuit diverts the current.

In extreme cases, static electricity or electromagnetic interference can cause unintended deployment.

Consequently, the SRS system enters fail-safe mode, illuminates the airbag warning light, and disables the passenger front airbag.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Passenger airbag wiring harness wear causing short to ground: Vibration chafes the harness insulation against the dashboard frame or air conditioning duct edge, allowing the exposed copper core to contact the vehicle body metal and form a parallel resistance.
  • 2Bent airbag connector pins or water ingress: Incorrect removal or installation causes the pins of the airbag connector (usually yellow, located inside the centre console or behind the glovebox) to touch the housing, or poor sealing causes electrolytic corrosion, forming a low-resistance path.
  • 3Clock spring internal short circuit: If the front passenger airbag features a steering wheel-mounted trigger mechanism (some models), a short circuit between the flat cable layers inside the clock spring reduces circuit resistance.
  • 4SRS control module internal sampling circuit fault: A damaged shunt resistor or A/D converter inside the ECU causes a false low-resistance fault, while the actual airbag circuit is normal.
  • 5Airbag inflator internal short circuit: Insulation failure between the igniter bridge wire and housing (manufacturing defect or moisture ingress) causes abnormally low resistance.
What To Do
  • 1
    Safety preparation: Switch off the ignition, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect the VDS diagnostic tool, read the freeze frame data (Fault Frame), record the vehicle status when the fault occurred, and confirm B161B1A is a current fault (Present) rather than a history fault.
  • 3
    Visual inspection: Remove the glovebox or passenger-side lower dashboard trim panel. Inspect the yellow airbag wiring harness for wear or crushing. Verify the connector is fully locked and check for water ingress or terminal oxidation.
  • 4
    Disconnect and isolate: Disconnect the front passenger airbag connector (usually located in the center of the dashboard or on the back of the airbag). Use a multimeter to measure the resistance on the wiring harness side (ECU side). A normal reading shows infinity or extremely high resistance (>10kΩ). Low resistance indicates a wiring harness short to ground.
  • 5
    Component test: If the wiring harness side is normal, connect a dedicated airbag load simulator (2.7Ω dummy resistor) to the ECU side. Clear the fault code. If the fault disappears, the SRS ECU is normal. Next, measure the airbag resistance. It must be between 2.0-5.0Ω. If it is below 1.5Ω, replace the airbag assembly.
  • 6
    Clock spring check: If equipped with a front passenger side clock spring, measure the internal slip ring resistance. The resistance must remain stable while turning the steering wheel. Replace the clock spring if intermittent low resistance occurs.
  • 7
    ECU verification: If the wiring harness, airbag, and clock spring are normal but the fault code persists, check for backed-out SRS ECU connector pins. Replace the SRS control module if necessary.
  • 8
    Repair verification: After repairing the short circuit or replacing the faulty component, reconnect all connectors and the 12V battery negative terminal. Use the VDS to perform 'Airbag System Configuration Check' and 'Sensor Calibration'. Clear the fault codes and perform a collision simulation test (activate test mode using the diagnostic tool; do not strike the vehicle directly). Verify DTC B161B1A does not return and the warning lamp is off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM dashboard wiring harness chafing causing intermittent low resistance

✓
A 2019 Qin Pro DM with 32,000 km intermittently displayed a 'Check Airbag' warning on the instrument cluster. VDS read B161B1A as an intermittent fault. Teardown inspection found the retaining clip for the passenger airbag wiring harness had come loose where it routes through the dashboard crossmember, allowing the harness to chafe against a sharp metal edge over time. The insulation wore through, exposing the copper core and creating a 0.8 ohm parallel resistance to ground. Re-wrapped the harness, fitted anti-chafe sleeving, and adjusted the routing to fix the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Passenger airbag connector water ingress corrosion case

✓
2018 Qin Pro petrol variant. Airbag warning light stayed on constantly after the vehicle waded through water; DTC B161B1A currently present. Inspection found the passenger airbag connector (located to the right of the evaporator housing) had a deteriorated seal. Water entry during wading caused electrolytic corrosion between the pins, creating a low-resistance path. Cleaned the connector terminals, applied electrical contact cleaner, and replaced the seal and connector housing. Fault resolved. Recommend checking the vehicle's water wading depth history.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal short circuit in airbag assembly caused abnormal resistance

✓
After an accident, a 2019 Qin PRO DM had its passenger airbag replaced with an aftermarket unit. After installation, DTC B161B1A set. Resistance measured normal on the harness side, but the new airbag measured only 0.6Ω, confirming an internal bridge wire short in the aftermarket gas generator. Replacing with a genuine part restored resistance to 2.8Ω. Cleared the DTC and it did not return. Must use genuine or certified parts; non-OEM airbags may have resistance deviations.
BYD DTC AI AnalysisFrom Chinese market (translated)

SRS ECU sampling circuit false fault

✓
2018 Qin Pro repeatedly logged DTC B161B1A, yet the airbag circuit resistance always measured normal at 2.4 Ω. Capturing the ECU detection pulses with an oscilloscope revealed a drift in the ECU’s internal sampling circuit reference voltage, causing it to falsely read low resistance. Replacing the SRS control module and recoding it—a step that requires writing the VIN and configuration code—permanently eliminated the fault. This is a rare case of control module hardware failure.
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]