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 — Seal U

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.

The B17FF-00 fault code on the Seal U indicates the airbag control unit is detecting an abnormal or missing vehicle speed signal. Severity is medium, as it can affect airbag timing or deployment decisions. Common causes include a faulty or dirty wheel speed sensor, damaged wiring, or corroded connectors. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wheel speed sensor (ABS sensor) component fault or contaminated sensor tip: internal coil open circuit, resistance drift (normal: 1.0-1.5 kΩ), or iron filings, mud, or sand covering the sensor tip, attenuating the magneto-electric signal and preventing the generation of sufficient pulse voltage (typically requires >0.5 V AC).
  • 2Physical damage to the vehicle speed signal transmission circuit: The wiring harness from the wheel speed sensor to the SRS ECU chafes and the insulation wears through at suspension movement interference points; 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 or ground, or abnormal terminating resistance (standard 60Ω), preventing the SRS ECU from verifying vehicle speed data via the bus.
  • 4SRS control unit internal signal processing circuit fault: A damaged vehicle speed signal acquisition chip, optocoupler isolation circuit, or A/D conversion module inside the ECU fails to correctly interpret 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 (Gateway) or instrument cluster fault: On models equipped with a gateway, the gateway drops packets when forwarding the vehicle speed signal, or a fault in the speedometer drive circuit inside the instrument cluster backfeeds into 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 (e.g., 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 tips. Remove any metal filings and oil contamination. 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 (must be >0.5 V and increase with wheel speed).
  • 3
    Disconnect the 12V battery negative terminal for 3 minutes, then unplug the SRS ECU connector (usually located 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 it is a 0-5V square wave without noise interference.
  • 4
    Measure resistance between pins 6 (CAN-H) and 14 (CAN-L) of the OBD-II diagnostic connector (standard: 60Ω±5Ω), CAN-H to ground voltage (2.5-3.5V), and CAN-L to ground voltage (1.5-2.5V). Check the connection status of the CAN wiring harness and the SRS ECU connector. Inspect for bus interference caused by aftermarket accessories (such as dash cams or audio equipment).
  • 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 (must 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 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.