AU
B161B-00

DTC B161B-00 indicates the airbag control unit (SRS ECU) detects the front passenger airbag (PAB) igniter circuit resistance is below the calibrated threshold (typically below 1 — Seal U

Safety System

DTC B161B-00 indicates the airbag control unit (SRS ECU) detects the front passenger airbag (PAB) igniter circuit resistance is below the calibrated threshold (typically below 1.5-2.0Ω, depending on the vehicle software version).

The standard SRS airbag igniter resistance is generally 2.0±0.5Ω.

Low resistance typically indicates a short circuit.

Potential causes include an internal short in the airbag igniter, a wiring harness short to ground, a short between connector terminals, or an internal short in the clock spring.

This fault forces the SRS system into a degraded mode.

The system may disable the front passenger airbag (preventing deployment) or, in extreme cases, risk unintended deployment.

When this DTC triggers, the instrument panel airbag warning light remains illuminated and the system halts collision detection for the front passenger airbag.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Front passenger frontal airbag module (inflator) internal igniter short circuit: Long-term use, moisture ingress, or manufacturing defects damage the igniter resistance wire insulation, causing resistance to drop below the threshold.
  • 2Clock spring internal short circuit: A short circuit in the flat cable inside the clock spring below the steering wheel causes an abnormal drop in airbag circuit resistance. This commonly occurs in high-mileage vehicles or from frequent steering wheel rotation.
  • 3Harness short to ground: Worn, crushed, or rodent-damaged wiring harness insulation inside the passenger-side dashboard causes the wire to contact body ground, creating a low-resistance path.
  • 4Connector terminal short circuit or corrosion: Water ingress, oxidation, or terminal deformation in the airbag wiring harness connector (yellow plug) causes a short circuit between terminals or from a terminal to the connector housing.
  • 5SRS ECU internal detection circuit fault: A fault in the airbag control unit internal sampling resistor or A/D conversion circuit causes a false low resistance reading (relatively rare; confirm only after ruling out external wiring).
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use a VDS2000, Launch X431, or similar diagnostic tool to read fault codes. Confirm B161B-00 is a current fault (Active) and not a history fault. Record the freeze frame data.
  • 3
    Visual inspection: Check the wiring harness around the front passenger side dashboard, glovebox and underneath the center console for obvious damage, water stains or rodent marks; check the yellow SRS connector for corrosion, looseness or backed-out terminals.
  • 4
    Circuit isolation test: Disconnect the front passenger airbag module connector (usually located on the back of the airbag module or behind the dashboard). Short the harness side of the connector using a dedicated SRS Shorting Bar or copper wire, and measure the harness circuit resistance. If the resistance returns to normal (around 2Ω), the fault is in the airbag module. If the resistance remains low, the fault is in the wiring harness or clock spring.
  • 5
    Clock spring inspection: Disconnect the clock spring from the SRS ECU and measure the resistance across the clock spring terminals. Normal resistance is 0-1Ω (continuity with very low resistance). If the resistance is abnormally low (<0.5Ω and unstable) or indicates a short circuit, replace the clock spring.
  • 6
    Harness continuity and insulation check: Use a multimeter to measure the airbag harness resistance to ground (should be infinite) and the end-to-end resistance of the harness (should be <1Ω). If the harness shows continuity to ground or a short circuit between wires, repair or replace the harness.
  • 7
    Component replacement: Replace the faulty component according to the above test results (front passenger airbag module, clock spring, wiring harness, or SRS ECU). When replacing the airbag module, use genuine parts and verify the new module resistance is within the standard range.
  • 8
    System reset and verification: Reconnect all connectors and the battery. Use the diagnostic tool to clear the fault codes. Perform an SRS system self-check (turn the ignition switch to ON and verify the airbag warning light turns off after 6 seconds). Calibrate the crash sensor (if required). Finally, perform a road test to verify the repair.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin EV300: Internal short circuit in passenger airbag module causing B161B-00

✓
A 2017 Qin EV300 with 80,000 km had the airbag warning light on steady. Scan tool pulled B161B-00 (front passenger airbag resistance too low) – current code. I disconnected the battery negative, waited 90 seconds, and removed the front passenger airbag module. Measured resistance at the module connector: only 0.8 Ω (normal is around 2.0 Ω) – clearly low. The harness side measured 2.1 Ω, within spec, so the fault was an internal igniter short in the module. Replaced the module with a genuine OEM unit, cleared the code, and ran a system self-check. Everything returned to normal, fault gone.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin 100: Clock spring short caused intermittent B161B-00

✓
2017 Qin 100. The customer reported the airbag warning light illuminating intermittently, especially after turning the steering wheel. The diagnostic tool retrieved current fault code B161B-00. Checked passenger airbag module resistance: normal. Measured clock spring output resistance and found fluctuating values—sometimes reading 0.3Ω (too low), sometimes normal. Disassembled the steering wheel for inspection and found the clock spring's internal flat cable worn from long-term rotation, causing a local short circuit. Replaced the clock spring assembly. After replacement, repeatedly turned the steering wheel to test; the fault did not reappear. Cleared B161B-00 and it has not returned.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV450 dashboard wiring harness chafed, short to ground

✓
2018 BYD Qin EV450. The SRS warning light came on after flood damage repairs. Retrieved DTC B161B-00. Checked below the passenger side dashboard and found the wiring harness retaining clip had detached. The harness had chafed against the metal dashboard bracket, damaging the insulation and causing the wire to short directly to ground. Measured airbag circuit resistance to ground at only 0.5 Ω. Repaired the damaged wiring by rewrapping with insulating tape and fitting corrugated tubing. Rerouted the harness and re-secured the clip. Cleared the fault code; system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Water ingress corroded the Qin 80 SRS connector, causing low resistance.

✓
2017 BYD Qin 80. Water accumulated below the front passenger-side A-pillar due to a windshield leak. The SRS warning light came on. Retrieved DTC B161B-00. Found obvious water stains and green copper corrosion inside the yellow SRS wiring harness connector below the A-pillar, with a micro short circuit between terminals. Measured resistance at 1.2Ω (below threshold). Cleaned the connector terminals with electronic contact cleaner, dried them with compressed air, applied conductive anti-corrosion compound, reconnected the connector, and sealed it against water ingress. Cleared the DTC and resolved the fault. Also repaired the windshield seal to prevent further water entry.
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]