AU
B161C

DTC B161C indicates the SRS (Supplemental Restraint System) ECU detects the front passenger frontal airbag ignition circuit resistance exceeds the calibrated upper limit (typically >5Ω) — Atto 8

Safety System

DTC B161C indicates the SRS (Supplemental Restraint System) ECU detects the front passenger frontal airbag ignition circuit resistance exceeds the calibrated upper limit (typically >5Ω).

Normal airbag igniter resistance is between 2.0Ω and 3.0Ω.

Excessive resistance indicates high resistance or an open circuit risk in the ignition circuit.

This prevents the ECU from supplying sufficient ignition current (typically 1.2A or higher) during a collision, causing the front passenger airbag to fail to deploy and severely compromising passive safety.

This is a hard fault.

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

Inspect and repair immediately.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Poor contact at pins 1 and 2 of front passenger airbag module connector X246 (located on the right side of the instrument panel cross beam), or black locating clip not fully seated (standard requirement: the top of the clip must sit below the terminal face).
  • 2A poor connection, oxidation, terminal back-out, or spread terminals in the wiring between the instrument panel harness and the airbag module causes increased contact resistance.
  • 3Aging, moisture ingress, or an internal open circuit in the front passenger airbag module squib causes increased resistance.
  • 4Prolonged parking in a high-humidity environment or driving through water causes internal connector corrosion, forming an oxide layer.
  • 5SRS ECU internal sampling resistor or A/D conversion circuit fault (intermittent resistance misjudgment; rule out by cross-checking).
What To Do
  • 1
    Safety preparation: Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the passenger-side lower dashboard trim panel and glove box. Locate airbag module connector X246. Check if the black locking clip sits lower than the terminal end (flush or protruding indicates incorrect installation). Confirm there is no looseness, backed-out pins, or signs of water ingress.
  • 3
    Resistance measurement: Disconnect connector X246. Use a digital multimeter to measure the resistance between the terminals on the airbag module side. The standard value is 2.0Ω-3.0Ω. If the resistance is >5Ω or infinite, this indicates an internal airbag module fault; replace the airbag module.
  • 4
    Circuit continuity test: Measure continuity between harness side X246-1 and the corresponding SRS ECU pin, and between X246-2 and ground. Circuit resistance must be <1Ω. Gently shake the wiring harness to check for intermittent open circuits.
  • 5
    Connector repair: If detecting poor contact, clean the pins with electrical contact cleaner and apply conductive grease. Use the dedicated terminal release tool to repair the terminal retaining spring. Reinstall the connector, verify the locking tab seats correctly, and confirm the insertion/withdrawal force is >50N.
  • 6
    System verification: Connect the battery. Use the VDS or ED300 diagnostic tool to clear the fault code. Perform an SRS system self-check (3 key cycles or a drive cycle). Verify B161C does not return and the warning light turns off. Read the data stream to confirm the front passenger airbag resistance is 2.0-3.0 Ω.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin: Poor contact at the X246 connector caused fault code B161C

✓
Symptoms: Airbag warning light stayed on after 3000 km, displaying a flash code: 5 seconds on, 7 flashes. Diagnosis: Connected the ED300 diagnostic tool and retrieved DTCs B161C (passenger airbag resistance too high) and B1610 (passenger airbag not connected). Isolated the fault to the passenger airbag module wiring harness, connector, or SRS ECU. Inspection: Checked the connection between the passenger airbag module pigtail and the instrument panel harness. Found poor contact at pins 1 and 2 of connector X246; the black retaining clip did not seat properly (the clip must sit below the terminal—flush or protruding indicates incorrect installation). Solution: Reassembled and secured pins 1 and 2 at X246, ensuring the black retaining clip seated properly below the terminal. Road tested after reassembly and the fault cleared.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Standard Diagnostic Procedure for SRS High Resistance – BYD Qin/Song/Yuan

✓
Symptoms: Dashboard airbag warning light stays on. DTC B161C-00 (front passenger airbag resistance high). Diagnosis: Per BYD Qin sedan workshop manual, B161C-00 indicates front passenger airbag resistance high. Diagnostic procedure: 1. Inspect front passenger airbag module and wiring harness connections. 2. Check connector X246 between the instrument panel harness and the airbag module (located on the instrument panel crossmember behind the glovebox). 3. Measure airbag module resistance. Normal resistance falls within specification (typically 2–5 ohms). High resistance indicates poor circuit connection or an internal airbag module fault. 4. Inspect connector pins for oxidation, looseness, or backing out. Repair: 1. Disconnect and reconnect the front passenger airbag module connector; secure it and ensure proper pin contact. 2. If the connector checks out okay but resistance remains high, replace the front passenger airbag module. 3. Clear fault codes and road test to verify.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Yuan EV front passenger airbag module internal igniter aging

✓
Symptoms: Intermittent airbag warning light on a 2019 Yuan EV at 50,000 km. Scanned DTC B161C (resistance too high). Diagnosis: Checked X246 connector; visually normal and secure. Measured wiring harness continuity at less than 0.5 Ω. Disconnected the airbag module and measured 8.5 Ω internal resistance, exceeding the 2–3 Ω specification. Determined the airbag module's internal igniter had aged, causing resistance drift. Fix: Replaced the genuine front passenger airbag module (part number varies by configuration). Post-replacement resistance 2.3 Ω. Reassembled components, cleared the fault code, and performed a crash simulation test with a resistive load substitute to confirm normal system operation.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM dashboard wiring harness pin backed out fault

✓
Symptoms: The airbag warning light on the 2021 Tang DM illuminates intermittently on rough roads and extinguishes when stationary. Retrieved historical DTC B161C. Diagnosis: Found intermittent fault. Removed the glovebox and inspected X246 connector. Pin 2 slightly backed out (~1 mm). Vehicle vibration caused poor contact with transient high resistance. Multimeter read normal resistance at rest, but the reading jumped above 10 Ω when moving the harness. Resolution: Used special terminal removal tool M101 to extract the terminal, repaired the contact spring tension, and reinserted it until an audible click confirmed lock. Measured mating force >50 N, meeting standard. Fault completely resolved.
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]