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B17A100

B17A100 is an internal diagnostic fault code for the BYD SRS (Supplemental Restraint System) control unit — Seal U

Safety System

B17A100 is an internal diagnostic fault code for the BYD SRS (Supplemental Restraint System) control unit. "Invalid Fault" indicates the airbag control module detects data frames from internal logic circuits, external crash sensors, or CAN bus communication containing format errors, CRC check failures, or values outside physically reasonable ranges during self-checks or real-time monitoring.

These conditions do not meet other specific fault definitions (such as open circuit, short circuit, or abnormal signal).

This fault typically indicates the ECU received "logically implausible" status information.

This forces the system into a safety fallback mode (e.g., airbag deactivation, pretensioner standby, or a continuously illuminated fault indicator), severely compromising crash protection functions.

In Qin PRO models, this fault commonly stems from ECU internal ADC reference voltage drift, momentary CAN bus interference, or marginal sensor signal values.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Electromagnetic interference or momentary short circuit on the CAN bus (powertrain or comfort network) causes the SRS ECU to receive corrupted data frames or incorrect node information.
  • 2Transient voltage drop in the vehicle power supply system (e.g., due to an aging battery during startup or generator regulator failure) causes abnormal ECU internal logic levels or EEPROM data checksum errors.
  • 3Front or side impact sensor internal resistance is marginal. Signal voltage fluctuates between 2.4V-2.6V, exceeding the ECU adaptive learning range.
  • 4Increased contact resistance at the clock spring (spiral cable) internal slip ring causes an abnormal driver-side airbag circuit signal. The ECU cannot identify a specific open or short circuit and reports the signal as invalid.
  • 5SRS control unit software version bug or hardware batch defect, common in early-production 2018 Qin PRO vehicles (software version below 201911); internal watchdog reset causes data overflow.
What To Do
  • 1
    Use the VDS2000/VDS3000 diagnostic tool to read the complete fault tree. Confirm if B17A100 is a current fault (Current DTC). Record key parameters in the freeze frame data, such as vehicle speed, voltage, and temperature. Check for accompanying U-class communication fault codes.
  • 2
    After disconnecting the battery negative terminal for 5 minutes, check the SRS ECU power supply and ground: measure the voltage drop between connector pin 16 (constant B+) and pin 8 (GND). Verify the static voltage is 12.4V-12.8V. Check fuses SB07 (10A) and FB10 (15A) for loose connections.
  • 3
    Check the CAN bus physical layer: measure pins 6 (CAN-H) and 14 (CAN-L) at the diagnostic port. Static voltage to ground should be 2.5 V ± 0.1 V, and resistance between the lines should be 60 Ω ± 5 Ω. Use an oscilloscope to check the bus waveform for spikes or bit stuffing errors. Rule out interference from aftermarket equipment (unshielded dash cams, modified audio systems).
  • 4
    Check the crash sensor circuit: Measure the resistance of the front crash sensor (B18, located on the radiator support) and the side crash sensor (B19, located below the B-pillar). The normal range is 2.0-3.0 kΩ. Check the wiring harness connectors for oxidation or water ingress. Measure the signal wire insulation resistance to ground; the value must be greater than 1 MΩ.
  • 5
    Perform software flashing and calibration: If hardware checks are normal, use the diagnostic tool to update the SRS ECU software (Qin PRO requires a version after November 2019). Perform 'Crash Sensor Zero Point Calibration' and 'Seat Occupancy Sensor Calibration'. Clear the fault codes, then perform a road test with 5 ignition cycles.
  • 6
    If the fault recurs during the road test, replace the SRS control unit assembly (part number: SC-3636100). After replacement, use the diagnostic tool to write the vehicle VIN and Configuration Code, and perform the safety system self-check again.
Real-World Cases
BYD DTC AI Analysis

CAN bus interference caused SRS data frame error

✓
A 2018 Qin PRO DM with 30,000 km intermittently displayed "Check SRS System" on the instrument cluster. The scan tool showed current DTC B17A100 and U015587 (communication fault with instrument cluster). Inspection found the owner-installed 360-degree camera system used untwisted CAN wires bundled parallel to the SRS harness. Rewiring with shielded twisted pair cleared the fault. Analysis: Electromagnetic interference from unshielded signal lines caused the SRS ECU to receive erroneous data frames, triggering invalid failsafe protection.
BYD DTC AI Analysis

Battery aging causes transient voltage anomaly

✓
2019 Qin PRO Fuel. Airbag warning light on during cold start. Retrieved DTC B17A100 (current). Measured battery CCA at only 40% of rated value. Replaced battery; fault persisted. Further inspection revealed alternator regulator failure with voltage fluctuating between 11.2V and 15.1V at idle. Replaced alternator and reflashed SRS ECU software. Fault cleared. Analysis: Voltage transient drop caused EEPROM data checksum error in ECU, triggering invalid fault code.
BYD DTC AI Analysis

False positive triggered by clock spring borderline resistance

✓
A 2018 Qin PRO DM had an intermittent airbag warning light when turning the steering wheel while stationary. The scan tool showed history DTC B17A100 with no other codes. Removing the steering wheel revealed wear on the clock spring (spiral cable) internal slip rings. The driver side airbag circuit resistance measured 2.8Ω–5.2Ω (normal <2.5Ω). Replaced the clock spring (PN: SC-3774200); multiple tests showed no fault recurrence. Analysis: Contact resistance sat at the ECU diagnostic threshold edge without registering as a specific open or short, resulting in an invalid fault.
BYD DTC AI Analysis

Software bug causing intermittent false positive

✓
2019 Qin PRO petrol, no modifications. Intermittent SRS warning light, DTC B17A100, no collision history. Checked power supply, ground, CAN bus and sensors; all normal. TSB indicates SRS software defect in this batch causing internal ADC reference voltage drift at -5°C to 5°C. Upgraded SRS ECU software to Ver.2019.11.2. Three-month follow-up, no recurrence.
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.