AU
B17A400

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

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.

The B17A400 fault code on the Seal U indicates an abnormal signal in the driver-side side airbag circuit, not an actual collision. Severity is medium because the side airbag or pretensioner may not work correctly in a crash. Common causes include a loose or corroded under-seat airbag connector, damaged wiring, or a faulty left side impact sensor. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Driver side side airbag module circuit fault: Includes a loose or oxidized airbag connector under the seat, backed-out pins, or an internal wire break resulting from repeated bending of the wiring harness during seat rail adjustment.
  • 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 contact at the driver-side seat belt pretensioner connector, wiring short circuit, or pretensioner internal resistance out of specification.
  • 4Airbag Control Unit (ACU) power supply/ground fault: Poor contact in the ACU constant power (B+), ignition power (IGN) or ground (GND) circuit causes the hardwired signal acquisition reference voltage to drift.
  • 5Intermediate wiring harness connector issue: Wiring harness connectors inside the vehicle's left door sill panel (such as GJ301, GJ302) suffer from moisture or corrosion, or the vehicle previously drove through water, causing terminal oxidation.
What To Do
  • 1
    Use the BYD VDS2000 or ED400 diagnostic tool to read all DTCs. Confirm B17A400 is a Current fault, not a History fault. Record the resistance or voltage value in the freeze frame data.
  • 2
    Perform safety procedure: Disconnect the battery negative terminal and wait at least 90 seconds for complete system discharge. Inspect 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 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; >10 Ω or infinity indicates an open circuit or high resistance.
  • 4
    Check the side impact sensor (SIS) inside the left B-pillar trim panel and verify the mounting bolt torque meets the specification (typically 8-10 N·m). Measure the sensor signal wire voltage to ground (0 V static, 5 V reference voltage with ignition ON).
  • 5
    Inspect the left door sill wiring harness, specifically checking for wear on the harness sleeve near the seat rail mounting point. Check the clearance between the wiring harness and the body metal edge. Repair any damage and rewrap the corrugated conduit if necessary.
  • 6
    If wiring measurements are normal, swap the left and right side impact sensors to cross-check. If the fault code moves with the sensor (changing to B17A500 front passenger side fault), replace the faulty sensor.
  • 7
    Check the voltage drop of the ACU power supply (constant B+, IGN) and ground (GND) circuits. Use the voltage drop test method to verify the voltage drop is less than 0.5V. Check the SCU fuse (usually 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 Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U overview →
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.