AU
B1717

DTC B1717 indicates a loss of communication or an open circuit between the driver-side knee airbag and the SRS (Supplemental Restraint System) control unit — Seal U

Safety System

DTC B1717 indicates a loss of communication or an open circuit between the driver-side knee airbag and the SRS (Supplemental Restraint System) control unit.

Specifically, this fault indicates an incorrect connection at the knee airbag module located under the left side of the dashboard, an open circuit in the wiring, or an internal open circuit in the airbag squib.

The knee airbag, a critical component of the frontal impact protection system, limits the forward movement of the driver's lower limbs and distributes crash forces.

When this fault occurs, the SRS control unit illuminates the airbag warning light and may enter fail-safe mode, disabling the related airbag circuit to prevent accidental deployment.

Consequently, the knee airbag will fail to deploy during a collision, increasing the risk of lower limb injury to the driver.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose knee airbag module connector, connector not fully seated, or locking mechanism failure (common after failing to reconnect following dashboard repairs, cabin air filter replacement, or carpet removal and installation)
  • 2Knee airbag wiring harness open circuit, chafing, or crush damage (especially at harness bends such as below the steering column and along the edge of the instrument panel frame)
  • 3Open circuit in knee airbag assembly inflator igniter (abnormal resistance; normally approx. 2.0-3.0 Ω)
  • 4Clock spring or dedicated wiring harness fault between the SRS control unit and the knee airbag.
  • 5Vehicle water ingress or a high-humidity environment causes corrosion or oxidation of the airbag connector terminals, resulting in excessive contact resistance.
What To Do
  • 1
    Use the BYD VDS or a dedicated diagnostic tool to read and confirm DTC B1717, check for other accompanying SRS fault codes, and record freeze frame data.
  • 2
    Turn the ignition switch to OFF, disconnect the battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 3
    Remove the driver side dashboard lower trim panel. Visually inspect the white/yellow connector on the knee airbag module (located under the left side of the dashboard) for a secure connection. Verify the locking tab engages fully. Disconnect and reconnect the connector, confirming a 'click' sound.
  • 4
    Disconnect the knee airbag connector. Use a multimeter to measure the resistance between the airbag terminals (specified range: typically 2.0-3.0 Ω). If the resistance is infinite, replace the airbag assembly. If the resistance is normal, measure continuity between the wiring harness end and the SRS ECU to check for open circuits or shorts to ground/power.
  • 5
    Check the wiring harness sleeve integrity, focusing on wear-prone areas around the steering column and above the pedals. Repair or replace the wiring harness if damaged. Route the harness correctly to prevent interference.
  • 6
    If connector terminals show corrosion, clean with electrical contact cleaner and apply conductive protective compound. If any terminal is backed out or deformed, repair or replace the connector.
  • 7
    Reconnect all components (ensure the airbag connectors are locked), connect the battery, and turn the ignition switch to the ON position. Use the diagnostic tool to clear the fault code, perform the SRS system self-check, and confirm B1717 does not return and the airbag warning light turns off.
  • 8
    Perform a road test for verification. Observe the knee airbag status data stream on the diagnostic tool (should display 'Connected/Normal'). If necessary, perform a simulated crash signal test (requires professional equipment).
Real-World Cases
BYD DTC AI Analysis

Knee airbag connector not reconnected after dashboard repair

✓
Symptoms: The BYD Qin owner reported the airbag warning light remained on after starting the vehicle. The scan tool retrieved DTC B1717 (left knee airbag disconnected). The vehicle had no collision history, but had recently had the cabin filter replaced and the blower motor serviced at a non-authorised workshop. Diagnosis: We removed the lower instrument panel trim and found the knee airbag white 2-pin connector unplugged, with the locking tab not engaged. The repairer had removed the trim but failed to reconnect the connector. Repair: We reconnected the knee airbag connector, fully engaging the locking tab. After clearing the DTC, the airbag light went out, the SRS system passed its self-check, and the live data stream showed the knee airbag status as 'Normal'.
Original source ↗
BYD DTC AI Analysis

Replaced knee airbag internal igniter due to open circuit

✓
Symptoms: BYD Tang DM owner reported that after startup the instrument cluster displayed 'Check Airbag System'. Scan tool retrieved DTC B1717. No accident history, but the vehicle had waded through water. Diagnosis: Disconnected battery negative terminal, waited 90 seconds. Removed knee airbag connector and measured resistance across airbag assembly terminals — open circuit (infinite resistance). Normal range: 2.0–3.0 Ω. Harness continuity normal, no short circuit. Fault traced to internal gas generator igniter failure in the knee airbag. Solution: Replaced driver-side knee airbag assembly (part number to be confirmed per VIN). Post-replacement resistance reading returned to normal. Reassembled, cleared DTCs, system normal.
Original source ↗
BYD DTC AI Analysis

Worn knee airbag wiring harness causing intermittent open circuit

✓
Symptoms: The BYD Song MAX owner reported the airbag warning light illuminated intermittently, sometimes going out while driving. The scan tool retrieved stored DTC B1717. Diagnosis: Checked the knee airbag connector — properly connected. Inspected the wiring harness routing and found it chafing against a metal bracket beneath the steering column. The insulation had worn through, partially breaking the copper wires and causing an intermittent open circuit when the vehicle vibrated. When measuring resistance while wiggling the harness, the reading jumped to infinite. Repair: Repaired the damaged harness by soldering the broken wires and insulating with heat shrink tubing. Re-routed the harness, fitted an abrasion-resistant protective sleeve, and secured it with cable ties to keep it away from the metal bracket. Replaced the damaged harness retaining clips. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Connector terminal backed out causing poor contact

✓
Symptoms: BYD e5 pure electric taxi. Airbag warning light suddenly came on while driving. Fault code: B1717. The carpet had been replaced before. Diagnosis: The knee airbag connector looked fine, but gently pulling the wiring harness caused the fault to reappear. Disconnecting the connector showed one terminal (usually the black wire) had backed out about 2mm from the housing, causing poor contact. The repair history indicated the connector was disconnected during carpet replacement. Misaligned reassembly pushed the terminal out. Resolution: Fixed the backed-out terminal using a specialised terminal tool, re-crimped it, and made sure it clicked securely into the connector housing. Rerouted and secured the floor harness so tension wouldn’t pull on the connector. Cleared the fault code and returned the vehicle. Followed up for a week; the fault did not recur.
Original source ↗
BYD DTC AI Analysis

Abnormal SRS control unit power supply caused false alarm

✓
Symptoms: BYD Yuan EV owner reported airbag warning light illuminates during cold starts. Fault code B1717 logged. Light occasionally turns off automatically once the vehicle warms up. Diagnosis: Checked knee airbag and wiring harness — no obvious abnormalities. Measured SRS control unit supply voltage dropping below 7V at startup (normal: above 9V). Found poor contact and oxidation at the SRS system power fuse holder in the engine compartment fuse box. Voltage between fuse holder and body ground unstable during startup. Solution: Replaced engine compartment fuse box (or repaired fuse holder contact surfaces). Cleaned and tightened SRS control unit ground point (typically on instrument panel frame). One-month follow-up: owner reported no recurrence.
Original source ↗
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.