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B17A300

In the BYD SRS system, DTC B17A300 carries two technical indications: 1) The surface description, "seat belt pretensioner collision", indicates the system detects a trigger signal or ignition circuit fault in the driver or passenger seat belt pretensioner (Pyrotechnic Pretensioner); 2) The underlying technical definition, "SRS CAN Signal Abnormal", means the airbag control unit (ACU) loses communication with the vehicle CAN network (typically the powertrain or comfort network) or detects a data checksum error — Seal 6 EV

Safety System

In the BYD SRS system, DTC B17A300 carries two technical indications: 1) The surface description, "seat belt pretensioner collision", indicates the system detects a trigger signal or ignition circuit fault in the driver or passenger seat belt pretensioner (Pyrotechnic Pretensioner); 2) The underlying technical definition, "SRS CAN Signal Abnormal", means the airbag control unit (ACU) loses communication with the vehicle CAN network (typically the powertrain or comfort network) or detects a data checksum error.

This fault forces the airbag system into a degraded mode, potentially preventing airbag and pretensioner deployment during a collision.

It also triggers a continuous airbag warning light on the instrument cluster.

In models such as the Qin PRO, this fault frequently accompanies B17A200 (collision record locked) or B17A400 (hardwired signal abnormal), indicating the vehicle experienced a collision or the CAN bus physical layer has an intermittent fault.

The B17A300 fault code on the Seal 6 EV indicates an SRS airbag system communication or seat belt pretensioner circuit problem. Severity is medium because airbags or pretensioners may not deploy correctly in a crash, and the airbag warning light may stay on. Common causes include CAN bus wiring faults, water-damaged harness connectors, or poor SRS ECU power or ground. 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 6 EV
  • 1CAN bus physical layer fault: Short circuit between CAN-H and CAN-L, short to power or ground, or terminal resistor (120Ω±2%) drift causing signal reflection. Typically occurs at dashboard wiring harness connectors or results from floor wiring harness oxidation following water ingress.
  • 2Airbag Control Unit (SRS ECU) power supply fault: Blown constant power (B+) circuit fuse, lost ignition switch signal (IGN), or loose ground points G301/G302 cause the ACU to lose power during the communication cycle.
  • 3Seat belt pretensioner ignition circuit fault: Water ingress and oxidation at the pretensioner connector (usually located below the B-pillar) cause abnormal resistance (normal: 2.0-2.4Ω), or a deployed but unreplaced pretensioner after a vehicle collision leaves the circuit open (>10Ω).
  • 4Internal control unit fault: Damaged ACU internal CAN transceiver chip (such as NXP TJA1042) or MCU clock crystal drift causing communication timing errors. Commonly results from voltage surges following battery depletion due to extended vehicle parking.
  • 5Software/configuration fault: The ACU software version does not match the vehicle network configuration table (DID Config), or failure to clear crash data using the 'Clear Crash Record' procedure on the dedicated diagnostic tool locks the system in a fault state.
What To Do
  • 1
    Safety preparation and initial inspection: Disconnect the 12V battery negative terminal and wait 3 minutes for the SRS capacitor to discharge. Use VDS or Launch X431 to read the complete DTC snapshot and check for accompanying B17A200 (crash lock) or B17A400 (hardwire fault) codes. Check the vehicle for collision repair history. Visually inspect the airbag module and pretensioner connectors for signs of deployment.
  • 2
    Power and ground verification: Reconnect the battery and turn the ignition to ON. Measure the voltage at ACU connector pin 1 (constant power B+) and pin 9 (IGN). The voltage must be 11-14V. Measure the resistance between the ground pin (usually pin 10/11) and the vehicle body. The resistance must be <1Ω. If the voltage is abnormal, check instrument panel distribution box fuses F1/9 and F2/3, and ground point G301.
  • 3
    CAN bus physical layer check: Use an oscilloscope to measure the ACU CAN-H (pin 6) and CAN-L (pin 14) waveforms. The dominant level should be CAN-H 3.5V / CAN-L 1.5V, and the recessive level 2.5V. Disconnect power and measure the termination resistance. Total vehicle resistance should be approximately 60Ω (two 120Ω resistors in parallel). If resistance is abnormal, inspect the wiring harness section by section for short or open circuits.
  • 4
    Pretensioner circuit check: Disconnect the pretensioner connector (driver side usually below the B-pillar; passenger side behind the glove box). Measure the pretensioner resistance. The value must be between 2.0 and 2.4Ω. Replace the pretensioner assembly if the circuit is open or shorted. Inspect the connector pins for oxidation (typically green copper corrosion). Clean with electronic contact cleaner if necessary.
  • 5
    Module replacement and calibration: If the wiring harness and pretensioner are normal, replace the ACU control unit (some models require VIN matching). After installing the new module, perform 'SRS system initialization' and 'crash sensor calibration'. Use a diagnostic tool to clear the DTC and perform a simulated crash test (substitute the airbag with a dedicated resistor load; never measure the airbag connector directly). Verify DTC B17A300 does not return and the instrument warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM SRS warning light on after driving through water, with DTC B17A300

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2019 BYD Qin PRO DM, 30,000 km. After driving through heavy flood water, the airbag warning light on the dash stayed on permanently. Scanned DTCs B17A300 and B17A200. Found the waterproof seal on the right front floor harness connector below the A-pillar was damaged. The CAN-H and CAN-L pins had oxidised, causing an intermittent short. Cleaned the oxide layer, applied conductive grease, and replaced the waterproof seal. CAN resistance now measured normal. Performed the collision record clear procedure. Fault resolved.
BYD DTC AI Analysis

Yuan PLUS communication fault caused by unreplaced pretensioner after accident repair

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2022 BYD Atto 3. After front collision repairs, the instrument cluster showed 'Safety System Fault'. DTCs: B17A300 (SRS CAN fault) and B165C00 (driver pretensioner open circuit). Inspection found the driver's seat belt pretensioner had deployed in the accident, but the repair shop only replaced the front bumper without replacing the seat belt assembly. The open pretensioner circuit caused the ACU to report a communication fault. Replaced the driver seat belt with force limiter assembly, performed online configuration and calibration. Fault resolved.
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BYD DTC AI Analysis

Qin Pro (Fuel): Loose ACU power supply connection causing intermittent fault

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2018 BYD Qin Pro petrol. Airbag warning light illuminated intermittently while driving. Scan tool showed history DTC B17A300. Checked ACU power supply; found ignition voltage dropped below 8V on rough roads. Traced wiring to loose F2/3 fuse holder below the dashboard, causing intermittent ACU reset and CAN communication timeout. Replaced instrument panel distribution box assembly and tightened all connectors. Fault did not recur.
BYD DTC AI Analysis

Software mismatch caused SRS system lockout

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After replacing the ACU module at the dealership, the 2019 Qin Pro DM showed an airbag fault on the instrument cluster. Read DTCs B17A300 and U0155 (lost communication with ACU). The new module had the correct part number but software version V1.2; the vehicle requires V2.1 to support the new network architecture. Used the BYD dedicated diagnostic tool to perform online programming, updated the ACU software to the latest version, wrote the VIN, and matched the configuration word. System returned to normal.
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.