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B17A400

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

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 — Qin Plus
  • 1Driver side airbag module circuit fault: Includes loose, oxidized, or backed-out pins in the under-seat airbag connector, or an internal wire break resulting from long-term wiring harness bending during seat track adjustment.
  • 2Left B-pillar side impact sensor (SIS) fault: Damaged internal piezoelectric element, loose mounting bolt causing poor ground, or connector water ingress and corrosion causing signal distortion.
  • 3Seat belt pretensioner circuit fault: poor contact at 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 affects the wiring harness connectors (e.g., GJ301, GJ302) inside the left door sill panel, or previous water wading caused 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 from the freeze frame data.
  • 2
    Perform the safety procedure: disconnect the negative battery terminal and wait at least 90 seconds to fully discharge the system. Inspect the white/yellow 2-pin side airbag module connector (usually marked SAB-D) 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. Normal value: 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. Verify the mounting bolt torque meets specification (typically 8-10 N·m). Measure the sensor signal wire voltage to ground (0V static; 5V reference voltage with ignition ON).
  • 5
    Inspect the left door sill wiring harness for wear, specifically the harness sleeve near the seat rail mounting point. Check the clearance between the wiring harness and the metal body edge. Repair as necessary and re-wrap the corrugated conduit.
  • 6
    If circuit measurements are normal, swap the left and right side impact sensors to cross-check. If the fault code transfers with 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. Use the voltage drop test method to verify the drop is less than 0.5V. Check the SCU fuse (usually 10A or 15A).
  • 8
    After eliminating all wiring, sensor, and power supply issues, replace the Airbag Control Unit (ACU). Perform 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 Qin Plus 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.