AU
B1631

DTC B1631 indicates a short to ground in the front passenger side airbag ignition circuit — Seal U

Safety System

DTC B1631 indicates a short to ground in the front passenger side airbag ignition circuit.

In the BYD SRS (Supplemental Restraint System), this fault code indicates the airbag control unit (ACU) detects an abnormally low resistance (typically <1Ω) between the front passenger side airbag (usually installed in the seat side or door trim panel) ignition wiring and body ground.

Normal airbag circuit resistance should measure between 2.0 and 3.0Ω.

This fault means: 1) the airbag may fail to deploy during a collision, resulting in a loss of side impact protection; 2) extreme cases pose a risk of unintended deployment; 3) the SRS system enters fail-safe mode, illuminating the instrument panel airbag warning light and potentially disabling other airbag functions.

This hard short circuit requires immediate repair to ensure occupant safety.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Front passenger side airbag module internal igniter short circuit: Internal squib terminals shorted to the housing due to moisture, aging, or manufacturing defects.
  • 2Wiring harness wear or crushing causing a short to ground: Long-term friction or compression damages the airbag wiring harness insulation at the seat rails, door hinges, or under the carpet, causing contact with vehicle body metal.
  • 3Connector water ingress or corrosion: Poor sealing of the airbag connector under the seat or in the B-pillar allows water ingress after washing the vehicle or wading, causing a short circuit between terminals or to ground.
  • 4SRS control module (ACU) internal fault: Damaged ACU internal drive circuit erroneously reports a short circuit fault code.
  • 5Improper repair work: During recent seat cover replacement or door and seat repairs, tools pierced the wiring harness or connectors failed to fully seat, causing a short circuit.
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS system capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Check that the front passenger seat side airbag (or door airbag) is visually intact. Inspect the yellow SRS wiring harness under the seat and inside the B-pillar trim for signs of abrasion, crushing, or puncture.
  • 3
    Connector check: Disconnect the airbag connector (use a shorting bar or wait for the capacitor to discharge). Check the terminals for oxidation, water ingress, or deformation. Measure the resistance to ground on the wiring harness side; the value must be infinite.
  • 4
    Airbag module test: Use a dedicated SRS tester or multimeter (high-impedance mode only) to measure airbag module resistance. Normal value: 2.0-3.0 Ω. If resistance is close to 0 Ω, replace the airbag.
  • 5
    Wiring harness continuity test: Test the airbag wiring harness between the ACU and the airbag in sections for continuity and insulation to ground. Repair damaged wiring or replace the wiring harness assembly.
  • 6
    System reset and verification: Reconnect all components and restore power. Use the VDS diagnostic tool to clear the fault code. Perform an SRS system self-check. Verify B1631 does not return and the airbag warning light turns off after the self-check.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Song Pro DM remote driving failure and steering angle sensor abnormality

✓
Symptoms: Remote driving function inoperative; no response from directional buttons. Diagnosis: VDS retrieved DTC B163100 (steering wheel angle signal abnormal). Root cause: steering wheel angle sensor not recalibrated after replacing the airbag (including clock spring), resulting in abnormal signal output. Solution: Recalibrated the steering wheel angle sensor using VDS. Cleared the DTC and the remote driving function returned to normal.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Tang DM: Engine self-starting in EV mode and erratic instrument cluster

✓
Symptoms: While driving in EV mode, engine started automatically, instrument cluster fault messages were erratic, recovered after power cycling. Diagnosis: VDS2000 scan found communication faults in multiple systems. Steering system logged DTC B163100 (steering angle sensor signal abnormal). Inspected the sensor connector — discovered oxidation and poor contact. Measured the wiring and detected intermittent voltage fluctuations. Resolution: Cleaned connector terminals and applied conductive grease. Reconnected and secured the wiring harness. Calibrated the steering angle sensor, which resolved the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Song Pro petrol: Intermittent HDC and tyre pressure monitoring warnings

✓
Symptoms: While driving, the instrument cluster intermittently displayed "Check HDC System" and "Check Tyre Pressure Monitoring System" warnings, and the warning lights came on intermittently. Diagnosis: A VDS scan found DTC B163100 (steering angle sensor related) and a body control module communication fault. Inspection confirmed a software abnormality and a loose connector on the right body domain controller, causing steering angle sensor signal processing errors. Resolution: Re-secured the right body domain controller connector, flashed the controller to the latest software version, and recalibrated the steering angle sensor. The fault cleared.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Song MAX: Difficulty shifting gears and ESP system warning

✓
Symptoms: Intermittent difficulty shifting gears; unable to shift out of Park with the brake pedal pressed. Dashboard displayed "Check ESP system" and "Check brake system". Diagnosis: VDS read DTC B163100 (steering angle sensor signal abnormal) and a brake pedal switch fault. The steering angle sensor was misaligned, and the signal deviation affected ESP and consequently the shift logic. Resolution: Reinstalled the steering angle sensor correctly, calibrated it, and tightened the brake pedal switch connector. Gear shifting returned to normal.
Original source ↗
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]