AU
B17A400

DTC B17A400 indicates the Supplemental Restraint System (SRS) detects an abnormal signal in the driver-side side airbag circuit or related hardwiring — Atto 3

Safety System

DTC B17A400 indicates the Supplemental Restraint System (SRS) detects an abnormal signal in the driver-side side airbag circuit or related hardwiring.

This DTC typically indicates an open circuit, short circuit, or out-of-range resistance (normal circuit resistance is typically 2.0-5.0Ω) in the hardwired communication between the Airbag Control Unit (ACU) and the driver-side side airbag module (SAB-D), left side impact sensor (SIS), or seat belt pretensioner.

This fault can prevent the driver-side side airbag from deploying during an actual collision or trigger the fault warning lamp without a collision, severely compromising passive safety system functionality.

The literal fault description reads 'driver side collision'; however, this indicates a side airbag system circuit anomaly, not an actual collision event.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Driver-side side airbag module circuit fault: Includes loose, oxidized, or backed-out pins at the airbag connector under the seat, or long-term bending of the wiring harness during seat track adjustment causing an internal wire break.
  • 2Left B-pillar side impact sensor (SIS) fault: damaged internal piezoelectric element, loose mounting bolts causing poor ground, or water ingress and corrosion in the connector causing signal distortion.
  • 3Seat belt pretensioner circuit fault: Poor connection at the driver-side seat belt pretensioner connector, wiring short circuit, or pretensioner resistance deviation.
  • 4Airbag Control Unit (ACU) power supply/ground fault: Poor contact in the ACU constant power (B+), ignition power (IGN), or ground (GND) circuits causes the hardwire signal acquisition reference voltage to drift.
  • 5Intermediate wiring harness connector issue: Moisture or corrosion in the wiring harness connectors inside the left door sill panel (such as GJ301, GJ302), or terminal oxidation from the vehicle previously driving through water.
What To Do
  • 1
    Use the BYD VDS2000 or ED400 diagnostic tool to read the complete DTC. Confirm B17A400 is a Current fault, not a History fault. Record the resistance or voltage value from the freeze frame data.
  • 2
    Perform safety procedure: Disconnect the battery negative terminal and wait at least 90 seconds to ensure complete system discharge. Check the white/yellow 2-pin connector (usually marked SAB-D) for the side airbag module under the driver's seat for looseness, backed-out pins, or oxidation. If necessary, clean the connector with electrical contact cleaner, apply conductive grease, and reconnect.
  • 3
    Use a multimeter to measure the driver-side airbag circuit resistance at the ACU connector. The normal value is 2.0-5.0 Ω. A reading <1 Ω indicates a short circuit; a reading >10 Ω or infinite indicates an open circuit or high resistance.
  • 4
    Check the side impact sensor (SIS) inside the left B-pillar trim panel. Verify the mounting bolt torque meets the specification (typically 8-10 N·m). Measure the sensor signal wire voltage to ground (normally 0V static, 5V reference voltage with ignition ON).
  • 5
    Inspect the left door sill wiring harness, specifically checking the harness sleeve near the seat rail mounting point for wear. Check the clearance between the wiring harness and the metal body edge. Repair any damage and rewrap the corrugated conduit if necessary.
  • 6
    If circuit measurements are normal, swap the left and right side impact sensors for cross-verification. If the fault code follows the sensor (changes to B17A500 front passenger side fault), replace the faulty sensor.
  • 7
    Check the voltage drop on the ACU power supply (constant B+, IGN) and ground (GND) circuits. Perform a voltage drop test to verify the drop is less than 0.5V. Check the SCU fuse (typically 10A or 15A).
  • 8
    After ruling out all wiring, sensor, and power supply faults, replace the Airbag Control Unit (ACU) and complete configuration coding, VIN writing, and system calibration using the OEM diagnostic tool.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM seat wiring harness chafing caused open circuit

✓
A 2019 Qin Pro DM at 32,000 km showed a constant SRS warning light. VDS read DTC B17A400 (current fault). Inspection found the wiring harness beneath the driver's seat rubbing against the seat height adjuster track. Long-term wear broke the airbag circuit wire internally while the insulation remained intact. Located the break after stripping the harness, repaired it with dedicated crimp terminals, and rerouted the wiring (added retaining clips to prevent track interference). Circuit resistance measured 3.2Ω after repair. Fault cleared.
BYD DTC AI Analysis

Yuan Plus: Simultaneous hardwire and CAN signal faults after collision

✓
After minor impact damage to the left B-pillar on a BYD Yuan Plus (Atto 3), the SRS warning light illuminated. The scan tool retrieved DTCs B17A400 (SRS Hardwire Signal Abnormal) and B17A300 (SRS CAN Signal Abnormal). Inspection revealed the left B-pillar side impact sensor connector had not fully locked; internal pins were slightly deformed from the impact, causing poor contact. Repaired the connector terminals and retightened the sensor mounting bolt to 9 N·m. Cleared the fault codes. The system self-test passed and the warning light extinguished.
Original source ↗
BYD DTC AI Analysis

Qin PLUS DM-i seatbelt pretensioner connector shorted after wading

✓
A Qin PLUS DM-i developed an SRS warning light after driving through floodwater in heavy rain. Scanned DTC B17A400. Live data showed driver's side circuit resistance at only 0.5Ω (abnormally low). Found the driver's seat belt pretensioner connector (located at the lowest point beneath the seat) had water ingress and oxidation, causing a short to ground. Cleaned the terminals, treated with WD-40 electrical contact cleaner, and blew dry. Resistance recovered to 2.5Ω. Also found the floor drain plugs blocked and cleared them to eliminate the risk.
BYD DTC AI Analysis

Poor airbag ECU ground on Song Pro EV caused signal abnormality

✓
The BYD Song Pro EV exhibited an intermittent SRS warning light, sometimes illuminating after driving over bumps. Diagnosis revealed DTC B17A400, but the fault cleared during every workshop inspection. Testing identified a poor connection at the airbag control unit (ACU) ground wire G301: the nut was loose and the contact surface had paint. Tightening the ground nut to 15 N·m and grinding the contact surface to remove the paint restored the hardwire signal. After one month of monitoring showed no recurrence, the fault was confirmed as an intermittent hardwire signal abnormality caused by poor grounding.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.