AU
B161A

DTC B161A indicates the Airbag Control Unit (ACU) detects abnormally low resistance, approaching 0 Ω (typically <1 — Atto 8

Safety System

DTC B161A indicates the Airbag Control Unit (ACU) detects abnormally low resistance, approaching 0 Ω (typically <1.0 Ω), in the front passenger frontal airbag ignition circuit.

Normal airbag igniter resistance remains between 2.0-3.0 Ω.

A resistance of 0 Ω usually indicates a short to ground, a wire-to-wire short, or an internal short in the airbag module igniter.

This fault causes the SRS system to enter fail-safe mode: 1) The airbag may fail to deploy during a collision due to the short circuit, causing a loss of passive protection; 2) Short-circuit current may cause unintended airbag deployment in extreme cases; 3) The system illuminates the instrument cluster airbag warning light and may store related freeze frame data.

This is a hard fault (continuous) requiring immediate repair for occupant safety.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Front passenger side airbag module internal igniter short circuit: Moisture ingress, aging, or a manufacturing defect in the airbag igniter reduces internal resistance to almost 0.
  • 2Airbag wiring harness short to ground: Vibration wear or loose retaining clips damage the internal instrument panel or floor harness insulation, causing a short to body ground.
  • 3Wiring harness connector water ingress and oxidation: Vehicle wading or A/C condensate leakage causes a short circuit between the terminals of the yellow airbag connector (usually located on the right side of the center console, in the floor wiring harness, or behind the glove box).
  • 4Short circuit between wiring harnesses: Crushing damage causes wiring harnesses of different polarities to make direct contact, forming a short circuit loop.
  • 5ACU internal detection circuit fault: A faulty airbag control unit internal sampling resistor or detection chip causes a false resistance reading of 0.
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the negative battery terminal and wait at least 3 minutes (to fully discharge the SRS capacitor). Do not use powered equipment or tools generating electromagnetic interference near the airbag wiring harness.
  • 2
    Visual inspection: Check the front passenger airbag connector (usually located behind the right side of the dashboard, in the floor wiring harness, or under the seat) for oxidation, water ingress, or deformed pins. Check the wiring harness for signs of abrasion, crushing, or damage.
  • 3
    Measure airbag module resistance: Carefully remove the front passenger airbag module (usually requires removing the right dashboard trim panel or glove box). Disconnect the airbag connector and measure the resistance directly across the two airbag module terminals. Normal value: 2.0-3.0Ω. If the resistance is close to 0Ω or <1.0Ω, replace the airbag module.
  • 4
    Measure the wiring harness in sections: Disconnect the ACU (Airbag Control Unit) connector and the airbag-side connector. Measure the resistance to ground at the harness-side connector; the value must be infinite (OL). Measure continuity between both ends of the harness to confirm no short to ground or short between wires.
  • 5
    Check the instrument panel wiring harness: Inspect the contact points between the instrument panel frame and the wiring harness. The front passenger side has no clock spring, but inspect the wiring harness for wear near the steering column or mounting brackets.
  • 6
    ACU inspection: If the wiring harness and module are normal, inspect the ACU connector pins for pushback or corrosion. Measure resistance between the corresponding internal ACU pins (specialized equipment required). Replace the ACU or reflash the software if necessary.
  • 7
    Repair verification: After repair, reconnect all components (ensure connector locking tabs engage fully). Restore the battery connection. Use the diagnostic tool to clear the fault code. Perform an SRS system self-check (3 ignition cycles). Confirm the fault does not return and the warning light turns off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Poor contact in the passenger side airbag wiring harness causing intermittent short circuit.

✓
Symptoms: The airbag warning light came on suddenly while driving and stayed on after restarting. I scanned the car with a diagnostic tool and found DTC B161A (passenger airbag circuit resistance too low), which wouldn't clear. Diagnosis: After disconnecting the negative battery terminal and waiting three minutes, I removed the passenger-side airbag module. I measured the resistance across the airbag plug terminals at 0.5 Ω (too low). Then I measured at the passenger airbag harness plug under the dashboard and got 0.2 Ω. When I wiggled the harness, the resistance reading became intermittent. Long-term vibration had worn through the insulation on the dashboard wiring, causing an intermittent short to ground. Resolution: I replaced the damaged harness section (from the ACU to the airbag), protected it with heat-resistant corrugated tubing, reconnected all connectors, cleared the fault codes, and ran the airbag system self-test. Fault fixed.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Water ingress caused the passenger airbag connector to oxidise and short circuit.

✓
Symptoms: After driving through water approximately 30cm deep, the airbag warning light stayed on. Read fault code B161A (passenger airbag circuit short to ground/resistance too low) with a Launch X-431. Diagnosis: Inspected the passenger-side floor wiring harness and the harness connectors under the instrument panel. Found clear water residue and green corrosion inside the main airbag harness connector (yellow). The airbag module resistance measured normal, but found an abnormal low resistance (0Ω) between the connector terminals. Determined that water caused a short between the terminals. Repair: Cleaned the corroded connector with electronic contact cleaner, blew it dry, and applied conductive anti-corrosion grease. Replaced the connector lock with a waterproof one and rewrapped the harness with waterproof tape. Cleared the fault code and road-tested for 50km without the fault reappearing.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket equipment causing SRS signal interference, resulting in false alarms

✓
Symptoms: No accident history or water damage. The airbag warning light illuminated suddenly after routine maintenance. DTC B161A set intermittently. The light would come on while driving, then go out after restarting the engine. The diagnostic scanner displayed it as a historical fault. Diagnosis: Inspected the front passenger airbag module connector and wiring harness and found no abnormalities. Resistance measured 2.4 Ω (within normal range). Checked the vehicle modification history; the owner had recently installed an aftermarket dash cam beneath the centre console. The power tap interfered with the airbag system's low-current detection signal. Removed the aftermarket device and monitored for 3 days; fault did not reappear. Solution: Removed the incorrect power feed. Rerouted power to tap properly from the reading light circuit or ACC fuse and added a filter capacitor. Cleared fault codes and followed up for 1 month; no recurrence.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Front passenger airbag module internal fault

✓
Symptoms: Vehicle used for 5 years, mileage 80,000 km, airbag warning light suddenly illuminated. DTC B161A persisted, accompanied by B161B (on dual-stage airbag models). The vehicle had a minor front bumper collision before, but the airbags did not deploy. Diagnosis: Measured passenger-side airbag module resistance: 0.3 Ω (too low). Swapped driver and passenger airbag modules (where model allowed); the fault code moved with the module, confirming an internal short in the passenger-side airbag module. Disassembled the module and found moisture damage to the internal squib (owner had used a high-pressure washer on dashboard gaps, causing water ingress). Solution: Replaced passenger-side airbag module (VIN recoding required) and waterproofed the dashboard. After repair, used a diagnostic tool to write the airbag configuration and calibrate the 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. Sources: [1]