AU
B161C-00

DTC B161C-00 indicates the Supplemental Restraint System (SRS) control unit detected the front passenger airbag (PAB) ignition circuit resistance exceeds the normal upper limit — Atto 8

Safety System

DTC B161C-00 indicates the Supplemental Restraint System (SRS) control unit detected the front passenger airbag (PAB) ignition circuit resistance exceeds the normal upper limit.

In BYD SRS systems, the control unit continuously monitors each airbag squib resistance via a low-current detection circuit.

The normal range is typically 2.0-3.0Ω.

If the resistance exceeds approximately 6.0Ω (high-resistance threshold), the control unit logs a 'high resistance' fault.

During a collision, this fault may prevent or delay front passenger airbag deployment, severely compromising occupant passive safety.

High resistance in the ignition circuit causes this fault.

Potential root causes include poor contact, oxidized wiring, loose connectors, or an aging squib inside the airbag module.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Poor contact at the internal slip ring of the clock spring (spiral cable) or worn carbon brushes increases connection resistance between the steering wheel and the airbag wiring harness. This is the most common cause of this fault.
  • 2Front passenger airbag module connector (yellow dedicated connector) loose, pins backed out, or terminals oxidized/corroded, causing abnormal contact resistance.
  • 3Vibration and chafing inside the dashboard damage the airbag wiring harness insulation. The copper wire partially breaks but does not completely sever, creating a high-resistance point.
  • 4Aging or moisture ingress in the front passenger airbag module internal squib causes its inherent resistance to drift beyond the permitted range.
  • 5SRS control unit internal sampling circuit fault or loose ground point causing an abnormal resistance detection reference.
What To Do
  • 1
    Safety preparation: Power down the vehicle, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS backup power supply and prevent accidental airbag deployment during repair.
  • 2
    Visual inspection: Inspect the front passenger airbag module for impact damage. Check that the yellow airbag connector on the instrument panel is fully connected and the locking tab is engaged. Inspect the wiring harness for crushing or abrasion.
  • 3
    Resistance measurement: Use a dedicated airbag resistance meter (or a digital multimeter on the low-resistance setting) to measure the front passenger airbag ignition circuit resistance. First, disconnect the battery and unplug the SRS ECU connector. Measure the resistance between the pins of the front passenger airbag circuit. Standard resistance is 2.0-3.0 Ω. If the resistance exceeds 6 Ω, confirm the fault.
  • 4
    Fault isolation: Disconnect the clock spring from the airbag module. Measure the resistance at the lower end (SRS ECU side) and upper end (airbag side) of the clock spring separately to determine whether the high resistance is in the clock spring, wiring harness, or airbag module itself.
  • 5
    Component test: For a suspected clock spring fault, measure its slip ring continuity. For a suspected airbag module fault, replace the airbag module with a dedicated airbag substitute resistor (2Ω) and read the fault code. If the fault disappears, this confirms the airbag module is damaged.
  • 6
    Repair/Replace: Replace the faulty component (clock spring, airbag wiring harness, or airbag module) based on the inspection results. Note: When replacing the airbag module, install new fixing bolts and tighten to the standard torque (usually 8-10 N·m).
  • 7
    System reset: Reconnect all connectors, connect the 12V battery, clear the fault code using the BYD dedicated diagnostic tool (VDS2000 or Launch X431), and perform the 'SRS system self-check' and 'configuration information write' (if installing a new airbag module).
  • 8
    Function verification: Perform a static test (turn the ignition switch ON and confirm the airbag warning lamp turns off after self-check) and a dynamic test (lightly tap the vehicle body near the crash sensor and observe if the airbag resistance value in the data stream remains stable). Finally, perform a road test to confirm.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Worn clock spring carbon brushes caused intermittent high resistance

✓
A 2018 Qin EV450's instrument cluster airbag warning light illuminated intermittently, logging DTC B161C-00. The fault appeared on cold starts and occasionally cleared when warm. Technicians measured the passenger airbag circuit resistance and found it fluctuating between 8-15Ω when cold, returning to normal once warm. Removing the steering wheel to inspect the clock spring, they found black carbon dust buildup on the internal slip rings and severe carbon brush wear. After replacing the clock spring (part number: K9HS-3463100), resistance returned to 2.3Ω and the fault cleared. The clock spring grease had dried out after prolonged use, causing poor contact between the carbon brushes and slip rings and resistance drift.
BYD DTC AI AnalysisFrom Chinese market (translated)

Airbag connector terminal oxidation increased contact resistance.

✓
2017 BYD Qin 100. After driving through water, the airbag warning light remained on and logged DTC B161C-00. Inspection found visible water stains inside the passenger side airbag connector (located on the right side of the dashboard), with terminals showing green oxidation. After cleaning the connector with electronic cleaner and sanding the terminals with fine sandpaper, the resistance still measured 5.8Ω. Replacing the airbag harness connector with a new one (with waterproof seal) cleared the fault. Check the A-pillar drain holes for blockages to prevent further water ingress.
BYD DTC AI AnalysisFrom Chinese market (translated)

Passenger airbag module internal squib aging

✓
2017 Qin EV300. Airbag warning light on at 80,000 km, DTC B161C-00. Measured airbag circuit resistance: infinite (open circuit). Resistance intermittently returned to normal after shaking the airbag module. Disconnected the clock spring and measured directly at the airbag module connector; resistance was unstable. Diagnosed as a dry solder joint on the internal igniter pins or moisture in the propellant. Replaced the passenger airbag module (part number: K9HS-5334100) and completed configuration coding; the system returned to normal. Dispose of the old airbag module according to dangerous goods recycling procedures.
BYD DTC AI AnalysisFrom Chinese market (translated)

Worn wiring harness behind the dashboard causing high resistance

✓
After accident repairs, DTC B161C-00 appeared. Inspection found improper dashboard removal and installation during the crash repair had trapped the passenger airbag harness against the dashboard metal bracket. The insulation chafed through and copper wires partially fractured, leaving only 2–3 strands connected. This ‘nearly broken’ state increased circuit resistance to 12 ohms. Repaired the damaged harness using 0.5mm² high-temperature wire, soldered joints, and double-layer heat-shrink insulation. Rerouted and secured the harness to maintain over 20mm clearance from metal edges. Fault cleared.
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]