AU
B17FF-00

DTC B17FF-00 indicates the airbag control unit (SRS ECU) continuously detects an abnormal vehicle speed pulse signal input or completely loses the vehicle speed signal — Atto 3

Safety System

DTC B17FF-00 indicates the airbag control unit (SRS ECU) continuously detects an abnormal vehicle speed pulse signal input or completely loses the vehicle speed signal.

In BYD Qin series vehicles, the SRS system receives the vehicle speed pulse signal from the wheel speed sensors (ABS sensors) or the vehicle control unit (VCU) via hardwire or the CAN bus.

The crash judgment algorithm uses this signal—the system determines the airbag deployment trigger threshold, ignition timing, and multi-stage airbag deployment intensity based on real-time vehicle speed.

The SRS ECU stores this DTC when it detects, within a set time window (typically exceeding 2-5 seconds), that the pulse signal frequency falls outside the valid range (such as the frequency corresponding to 0-255 km/h), the signal completely drops out, or the signal deviates significantly from the vehicle speed data transmitted on the CAN bus.

This fault forces the airbag system into Degradation Mode.

During a collision, the airbags may deploy late, fail to deploy, or deploy inadvertently at low speeds, severely compromising passive safety performance.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Wheel speed sensor (ABS sensor) component fault or contaminated tip: Sensor internal coil open circuit, resistance drift (normal 1.0-1.5kΩ), or metal shavings or mud covering the sensor attenuates the magnetic signal, preventing the generation of sufficient pulse voltage (typically requires >0.5V AC).
  • 2Physical damage to the vehicle speed signal transmission circuit: the wiring harness from the wheel speed sensor to the SRS ECU chafes and wears through the insulation at suspension movement interference points, or connector pins back out, oxidize, or suffer water ingress, causing an intermittent signal open circuit or short to ground.
  • 3CAN bus communication fault: Short circuit between the H and L lines of the Powertrain CAN or Body CAN, short to power/ground, or abnormal terminating resistance (standard 60Ω), preventing the SRS ECU from validating vehicle speed data via the bus.
  • 4SRS control unit internal signal processing circuit fault: Damage to the ECU internal vehicle speed signal acquisition chip, optocoupler isolation circuit, or A/D conversion module prevents correct interpretation of the input square-wave signal, or a voltage drop (>0.5V) in the ECU constant power supply (+B), ignition power supply (IG1), or ground (GND) causes an acquisition reference deviation.
  • 5Gateway controller or instrument cluster fault: On gateway-equipped models, the gateway drops packets when forwarding the vehicle speed signal, or an internal speedometer drive circuit fault in the instrument cluster feeds back and disrupts the signal source.
What To Do
  • 1
    Perform a full scan using the genuine BYD diagnostic tool VDS2000/VDS3100. Confirm whether B17FF-00 is an active or history fault. Read the freeze frame data to record the vehicle speed when the fault occurred. Simultaneously check for accompanying wheel speed sensor fault codes (such as the C0035-C0052 series) or CAN communication fault codes.
  • 2
    Raise the vehicle until the wheels are off the ground. Visually inspect the installation gap of the four wheel speed sensors (standard 0.3–1.2 mm) and the cleanliness of the sensor heads. Remove any metal shavings and oil. Use a multimeter to measure the sensor resistance (1.0–1.5 kΩ at 20°C). Turn the wheel by hand and observe the AC voltage output (>0.5 V, increasing with wheel speed).
  • 3
    Disconnect the 12V battery negative terminal for 3 minutes, then unplug the SRS ECU connector (usually under the center console or center tunnel). Check continuity between the vehicle speed signal input pin (refer to the wiring diagram, usually Pin 18 or a specific channel) and body ground. Measure the actual pulse waveform using an oscilloscope to verify a 0-5V square wave without noise interference.
  • 4
    Measure the resistance between pins 6 (CAN-H) and 14 (CAN-L) on the OBD-II diagnostic connector (standard: 60Ω±5Ω). Measure the CAN-H voltage to ground (2.5-3.5V) and CAN-L voltage to ground (1.5-2.5V). Check the connection between the CAN wiring harness and the SRS ECU connector. Inspect for aftermarket accessories (such as dash cams or audio equipment) causing bus interference.
  • 5
    If the wiring and sensor are normal, reconnect the connector and check the SRS ECU power supply and ground: measure the ECU connector +B pin voltage (should equal battery voltage, >12.4V), verify the IGN pin has 12V with the ignition ON, and verify the resistance between the GND pin and body ground is <1Ω. If all checks are normal, replace the SRS control unit. Use the OEM diagnostic tool to perform Online Coding to write the vehicle VIN, configuration parameters, and calibration data. Finally, perform an airbag system self-diagnosis and clear the fault codes.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 left front wheel speed sensor iron filings contamination

✓
2017 Qin EV300, 62,000 km. Airbag warning light constantly illuminated. Retrieved DTC B17FF-00 (current fault). Inspection found the left front wheel speed sensor head had accumulated a large amount of magnetic iron debris (from brake pad wear), causing signal amplitude attenuation. Cleaned the sensor surface and tone ring, used an oscilloscope to verify the output waveform had returned to normal, cleared the fault code and road-tested for 10 km with no recurrence. Advised the owner to check wheel speed sensor cleanliness every 20,000 km and avoid prolonged parking in strong magnetic environments.
BYD DTC AI Analysis

BYD Qin EV450 aftermarket audio installation caused CAN bus interference

✓
2018 BYD Qin EV450 developed an intermittent SRS warning light after a high-power amplifier was installed at a third-party workshop. DTC B17FF-00 set intermittently. Diagnosis found the amplifier power cable had not been routed separately, running parallel to the SRS CAN harness and causing electromagnetic interference. Rerouted the amplifier power cable (>10cm from the CAN bus), fitted a ferrite core filter at the SRS ECU connector, and connected the amplifier ground directly to the main body ground point. Fault fully resolved.
BYD DTC AI Analysis

BYD Qin 100 SRS control unit internal signal processing chip failure

✓
A 2017 Qin 100 had intermittent airbag warning light illumination on rough roads. VDS showed historical fault code B17FF-00 with a "Vehicle Speed Signal Unreliable" freeze frame. Checked all four wheel speed sensors and wiring harnesses; all normal. The vehicle speed signal waveform at the SRS ECU input was continuous with normal amplitude, but the ECU's internal data processing module failed intermittently (suspected cold solder joint). Replaced the airbag control unit (part number ...), performed online matching with VDS3100 (wrote VIN and configuration codes), and ran system self-learning. Tracked for one month; no recurrence. Some online sources incorrectly associate this fault code with the high voltage battery system; it actually indicates an SRS vehicle speed signal fault.
Original source ↗
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.