AU
B161A1A

DTC B161A1A indicates the Supplemental Restraint System (SRS) detects the front passenger airbag (PAB) ignition circuit resistance is 0 ohms or below the threshold (usually <0 — Seal U

Safety System

DTC B161A1A indicates the Supplemental Restraint System (SRS) detects the front passenger airbag (PAB) ignition circuit resistance is 0 ohms or below the threshold (usually <0.8Ω).

The SRS ECU monitors circuit integrity using a constant current source to measure the squib circuit resistance.

Normal resistance is 1.5-3.5Ω (typical value 2.0-2.8Ω).

A resistance of 0 indicates a short circuit.

Possible causes include an internal short in the airbag module squib, an internal short in the clock spring, a wiring harness short to ground or power, or a faulty internal sampling circuit in the SRS ECU.

This fault prevents the front passenger airbag from deploying during a collision (fail-safe mode) or causes unintentional deployment (extremely rare but dangerous).

The system illuminates the airbag warning light and disables the front passenger airbag.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Front passenger airbag module internal igniter short circuit: Short circuit in the airbag internal bridge wire or moisture in the pyrotechnic charge causes conduction between terminals.
  • 2Clock spring (spiral cable) internal short circuit: Damage to the spiral cable winding beneath the steering wheel, or a broken internal ribbon cable causing a short to ground or short between terminals.
  • 3Physical damage to the wiring harness: Sharp edges cut or pinch the wiring harness inside the dashboard, causing a short circuit to body ground or the 12V power line.
  • 4Connector fault: Airbag connector (usually yellow) has bent terminals, backed-out pins, corrosion from water ingress, or foreign metallic debris causing a short circuit between terminals.
  • 5SRS ECU internal fault: Damaged A/D converter in the airbag control unit internal sampling circuit, or driver chip short circuit.
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the 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 diagnostic tool and read the freeze frame data. Confirm the fault is Current, not a historical fault, and record the environmental data at the time of the fault.
  • 3
    Visual inspection: Check the front passenger airbag module connector (usually located on the right side of the dashboard or behind the glove box) for oxidation, water ingress, or bent pins; check the clock spring connector.
  • 4
    Isolation diagnosis: Disconnect the front passenger airbag module connector and use a multimeter to measure the resistance between the pins on the airbag module side. If the resistance is 0Ω, replace the airbag module. If the resistance is within the normal range (2-3Ω), the fault lies in the wiring harness or ECU.
  • 5
    Harness continuity check: Disconnect the SRS ECU connector and measure the harness between the ECU and airbag connector. Check for short to ground (resistance between pin and vehicle body), short to power (resistance between pin and 12V), and short between wires (resistance between high-side and low-side pins).
  • 6
    Clock spring inspection (if applicable): For circuits integrated into the clock spring, measure the resistance between the clock spring input and output terminals. The resistance must remain stable when turning the steering wheel. If the reading is 0Ω or fluctuates, replace the clock spring.
  • 7
    ECU verification: If the wiring harness and airbag module are normal, measure the corresponding SRS ECU pin output. If a short circuit condition remains, replace the SRS ECU and perform coding and matching.
  • 8
    Repair and verification: After repairing or replacing the faulty component, reconnect all connectors and restore power. Use the diagnostic tool to clear the fault code and execute the 'Deployment Control Unit Check' or 'Crash Output Check' function. Confirm the current fault changes to 'Normal' and the fault lamp turns off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin EV: Passenger airbag connector short-circuited due to water ingress

✓
After driving through water, the instrument panel airbag warning light stayed on. Retrieved DTC B161A1A. Inspection found the passenger airbag connector (behind the glovebox) had a deteriorated seal. Water inside caused a short between the terminals, measuring 0.3 Ω. Disassembled the connector, cleaned and dried it, applied conductive anti-corrosion compound, and replaced it with an improved waterproof connector. Resistance returned to 2.4 Ω, resolving the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal short circuit in BYD E3 clock spring caused zero resistance.

✓
The customer reported a noise when turning the steering wheel, after which the airbag warning light came on. The scan tool showed code B161A1A. After disconnecting the passenger airbag module, the module itself tested normal, but the harness side still measured as short-circuited. Further inspection of the clock spring (spiral cable) found that the internal flexible ribbon cable had broken and grounded out, creating a short to ground in the circuit. Replacing the clock spring assembly resolved the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD E2 dashboard wiring harness chafed, short to earth

✓
After driving on rough roads, the airbag warning light illuminated intermittently. Freeze frame data showed DTC B161A1A. Inspection found a sharp edge on the right side of the instrument panel bracket. The passenger airbag wiring harness (yellow) had chafed against this edge, damaging the insulation and causing the copper wires to short to ground on the metal bracket. Repaired the harness (re-wrapped), fitted a rubber protective sleeve to the bracket edge, and rerouted the wiring to prevent further contact.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin EV SRS ECU sampling circuit fault

✓
After replacing the front windscreen (involving dashboard removal and refitting), DTC B161A1A appeared. Measured passenger airbag module resistance: 2.6 Ω (normal). Harness continuity ok, no shorts to earth or power. Suspected internal SRS ECU fault. Tried replacing with a same-model ECU (requires syncing VIN and coding data). Fault code cleared and hasn't returned. The original ECU had a damaged internal driver chip that falsely reported a short circuit.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD E3 front passenger airbag module internal igniter short circuit

✓
Replaced the passenger airbag after the accident. After installation, DTC B161A1A set. Disconnected the airbag connector and measured resistance across the new airbag module pins at 0.8 Ω (below normal). Determined a part quality issue (internal bridge wire short circuit or manufacturing defect). Installed a genuine OEM airbag module; measured resistance at 2.2 Ω, and the system self‑test passed.
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]