AU
B161B

DTC B161B indicates the Airbag Control Module (ACM) detects the Passenger Airbag (PAB) igniter (inflator) resistance is below the system-calibrated lower threshold (typically below 1 — Seal U

Safety System

DTC B161B indicates the Airbag Control Module (ACM) detects the Passenger Airbag (PAB) igniter (inflator) resistance is below the system-calibrated lower threshold (typically below 1.0–1.5 Ω; normal range is 1.5–3.5 Ω).

This fault represents an abnormal electrical characteristic in the SRS circuit or components.

Potential causes include an internal short circuit in the igniter, a wiring harness short to ground, a short between connector pins, or a faulty internal detection circuit within the control module.

Upon detecting this fault, the system enters fail-safe mode and illuminates the airbag warning lamp.

This condition compromises occupant safety; during a collision, the passenger airbag may fail to deploy (fail-safe) or, in rare cases, deploy unexpectedly due to false triggering.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Water ingress, corrosion, or pin deformation in the front passenger airbag wiring harness connector causes a short circuit between the positive and negative pins, significantly reducing measured resistance.
  • 2Damaged insulation on the wiring harness between the Airbag Control Module (ACM) and the front passenger airbag, causing a short to body ground or short to power.
  • 3Front passenger airbag assembly (inflator): Moisture in the internal igniter or a manufacturing defect causes an abnormal decrease in bridge wire resistance.
  • 4Instrument panel internal wiring harness pinched or abraded during assembly or subsequent repairs, causing a short circuit between multi-core wires.
  • 5Airbag control module internal sampling circuit fault or software calibration error causing detected resistance values to drift (false positive fault).
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS or EDT) to read the fault code, confirm whether B161B is a current fault (Active) or a history fault (History), and record the freeze frame data.
  • 2
    Perform safety procedure: disconnect the battery negative terminal and wait at least 90 seconds to discharge residual voltage in the SRS system to prevent accidental airbag deployment.
  • 3
    Remove the front passenger dashboard trim panel. Inspect the airbag wiring harness connector (usually located behind the glove box or on the dashboard frame) for looseness, water ingress, corrosion, or foreign objects causing a short circuit between pins. Clean or repair the connector.
  • 4
    Disconnect the front passenger airbag connector. Use a multimeter to measure the resistance on the airbag harness side (from the ACM to the connector). Resistance should be infinite to ground and infinite between the wires. If continuity exists, the harness has a short circuit. Repair the harness.
  • 5
    Measure the resistance of the front passenger airbag assembly (inflator). The value should be within the standard range (usually 2-3Ω). If the resistance is too low (<1Ω), it indicates an internal short circuit in the airbag assembly. Replace the front passenger airbag module.
  • 6
    Inspect the routing of the SRS main wiring harness inside the instrument panel for signs of abrasion, pinching, or interference with body metal. Repair with insulating tape or replace the wiring harness if necessary.
  • 7
    If the wiring harness and airbag are normal, check the Airbag Control Module (ACM) power supply, ground, and communication lines. If necessary, update the ACM software or replace the control module.
  • 8
    After completing the repair, reconnect all connectors and the battery. Clear the fault code, turn the ignition switch to ON, and verify the SRS warning lamp turns off after 6 seconds to confirm a successful system self-check.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Water ingress into the Song MAX dashboard shorted the airbag connector.

✓
A 2019 BYD Song MAX reported DTC B161B. Inspection found that after the front windscreen was replaced, poor sealing allowed rainwater to seep into the dashboard. Water entered the passenger airbag's blue 2-pin connector, causing electrolytic corrosion between the pins and a short circuit. Resistance measured just 0.3Ω. Removed the dashboard, thoroughly dried the wiring harness, cleaned the connector with electronic cleaner, applied conductive protectant, and replaced the airbag connector housing. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Modified seats on Yuan EV pinched wiring harness, causing abnormal resistance

✓
A 2019 Yuan EV showed code B161B. The vehicle had no accident history. Inspection found the owner had modified the front passenger electric seat. During installation, the owner did not properly secure the SRS wiring harness, causing the seat rail to crush it. The damaged insulation caused the wires to short to ground. Repair: Removed the seat, repaired the two damaged SRS wires (airbag circuit), rerouted the harness and secured it with cable ties in the wiring channel to prevent interference with moving parts. Cleared the code; it has not returned.
BYD DTC AI AnalysisFrom Chinese market (translated)

Tang DM airbag control module software false alarm

✓
2021 Tang DM: Airbag light came on intermittently while driving. Scan tool retrieved DTC B161B, but passenger airbag resistance was normal (2.1Ω) and the wiring harness had no shorts. Further diagnosis traced the fault to an early-batch ACM software calibration issue causing resistance sampling deviations under specific low-temperature conditions. Fix: Updated the airbag control module software using VDS2000 from V1.2 to V1.4. The fault has not recurred since the update.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro passenger airbag internal short circuit replacement case

✓
2020 BYD Qin (petrol). After accident repairs, the vehicle logged DTC B161B. The passenger airbag did not deploy in the crash, but disassembly revealed the airbag assembly had been impacted. The internal igniter bridge wire suffered damage, reducing resistance to 0.8Ω. Disconnected the airbag connector and measured the harness side: infinite resistance (normal), confirming the airbag unit was at fault. Fix: Replaced the OEM passenger airbag assembly (part number: ...), then performed module configuration and system self-test. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Song MAX wiring harness chafing against dashboard frame

✓
A 2019 Song MAX with 30,000 km had DTC B161B. Inspection found the SRS wiring harness inside the dashboard had not been routed according to standard during factory assembly. The harness chafed against a metal bracket over time, damaging the insulation and causing a short between two signal wires. The warning light would come on intermittently when driving over bumps. Repair: Repaired the damaged wires (2), wrapped with corrugated tubing, rerouted the harness to avoid the sharp bracket, fitted a protective rubber grommet, and ensured more than 20 mm clearance from metal components.
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]