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B1718

B1718 is a BYD-specific SRS (Supplemental Restraint System / airbag system) fault code indicating an unintended low-resistance path (short to ground) between the driver-side knee airbag (Left Knee Airbag) ignition circuit and vehicle ground (GND) — Seal 6 EV

Safety System

B1718 is a BYD-specific SRS (Supplemental Restraint System / airbag system) fault code indicating an unintended low-resistance path (short to ground) between the driver-side knee airbag (Left Knee Airbag) ignition circuit and vehicle ground (GND).

The knee airbag contains an igniter (squib).

Under normal conditions, both igniter terminals must show an open circuit (infinite resistance) to ground.

A short to ground indicates current may bypass the igniter and flow directly to ground, causing the airbag control unit (ACU) to register a fault in that airbag circuit.

This fault poses a severe safety risk.

The short circuit can prevent the airbag from deploying during a collision or, in extreme cases, trigger unintended deployment.

The system classifies this fault as severity level 3, illuminates the SRS warning lamp continuously, and may force the entire airbag system into fail-safe mode (disabling all airbags).

The B1718 fault code on the Seal 6 EV indicates a high-severity SRS fault: a short to ground in the driver-side knee airbag ignition circuit. This can stop the airbag from deploying or, rarely, cause unintended deployment, and may disable the airbag system. Common causes include damaged under-dash wiring or water/corrosion in the connector. Do not inspect it yourself; visit an authorised dealer. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Knee airbag wiring harness insulation damage: Long-term friction or crushing (e.g., driver knee impact or improper aftermarket pedal installation) damages the wiring harness under the steering wheel or inside the dashboard, causing the copper wire to contact the vehicle body metal.
  • 2Connector water ingress or corrosion: Water enters the knee airbag connector (usually located under the left side of the dashboard) due to driving through water, A/C condensate leakage, or car washing, causing a terminal-to-terminal or terminal-to-housing short circuit.
  • 3Airbag Control Unit (ACU) internal fault: Damaged ACU internal driver circuit or monitoring circuit triggers a false short-to-ground fault (actual wiring is normal).
  • 4Knee airbag assembly internal short circuit: Airbag igniter internal short circuit (very rare; typically exhibits abnormally low airbag resistance)
  • 5Improper repair procedures: Screws crushed or clips pierced the wiring harness during previous removal of the instrument panel or knee bolster, or improper securing during reassembly caused the harness to contact sharp metal edges.
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the 12V battery negative terminal and wait at least 90 seconds (to fully discharge the SRS capacitor and prevent accidental airbag deployment).
  • 2
    Visual inspection: Remove the driver-side knee trim panel (Under Cover). Check the knee airbag wiring harness (yellow sleeve) for crushing, cuts, or abrasion. Focus on contact points with the steering column and metal brackets.
  • 3
    Connector inspection: Disconnect the knee airbag connector (usually protected by a shorting bar/shorting spring). Check the terminals for water ingress, corrosion, burning, or deformation. Measure the resistance between each of the two terminals on the harness side of the connector and body ground. The normal reading is infinity (OL). A resistance less than 1Ω indicates a short circuit.
  • 4
    Wiring harness insulation test: Use a megohmmeter or multimeter high-resistance range to measure the insulation resistance to ground of the knee airbag circuit (from the airbag connector to the ACU connector). Resistance must be greater than 10MΩ.
  • 5
    Airbag unit test: After verifying the wiring is normal, measure the resistance between the two terminals of the knee airbag assembly (standard value is usually 2.0-3.0 Ω). Separately measure the resistance from each terminal to the airbag metal housing (should be infinite). If a terminal has continuity to the housing, replace the airbag assembly.
  • 6
    Fault repair: Replace the damaged wiring harness or repair the insulation (seal completely with heat-shrink tubing). Clean or replace corroded connectors. Secure the wiring harness retaining clips in place to prevent interference with the vehicle body.
  • 7
    System verification: Reconnect all components and the battery. Use the diagnostic tool to clear the fault code. Perform the SRS system self-test (usually involves cycling the ignition switch). Confirm B1718 does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Corroded knee airbag connector on water-damaged vehicle caused B1718

✓
After driving through heavy floodwater, a 2020 BYD Qin petrol's SRS warning light stayed on. Scanning revealed DTC B1718 (left knee airbag short to ground). The technician removed the driver's knee panel and found significant water staining and copper oxide corrosion inside the knee airbag connector under the left side of the steering column. The connector seal had deteriorated, allowing water to enter the terminal cavity during the flood and causing the terminals to short against the grounded connector housing. The technician cleaned the connector thoroughly with electronic contact cleaner, dried it, polished the terminals with fine sandpaper, applied conductive grease, and fitted a new waterproof seal. Reinstallation cleared the fault.
BYD DTC AI Analysis

Aftermarket metal pedal interference caused wiring harness wear

✓
After the owner of a 2021 BYD Tang DM installed aftermarket metal pedals, the airbag warning light occasionally illuminated while driving, and the diagnostic tool displayed DTC B1718. Inspection revealed the mounting screws for the modified pedals were too long and had pierced the knee airbag wiring harness (yellow harness) beneath the dashboard, causing the copper wires to intermittently short to chassis ground. Solution: Removed the non-compliant pedals. Repaired the damaged harness—cut out the damaged section, soldered the wires, and insulated with double-layer heat-shrink tubing. Re-routed the wiring along the standard path and secured it with OEM clips, ensuring adequate clearance from the pedal mechanism.
BYD DTC AI Analysis

Wiring harness incorrectly secured after accident repair caused short circuit

✓
A 2019 BYD Yuan EV returned one week after delivery following a front collision repair (dashboard replaced), with the airbag warning light on and DTC B1718 stored. Workshop inspection found that during reassembly, the technician had incorrectly trapped the knee airbag wiring harness under the dashboard metal bracket. The bracket’s sharp edge cut through the harness, exposing the internal wires and causing a short to ground. Replaced the damaged knee airbag harness assembly (too damaged to repair). Re-routed the wiring strictly according to the workshop manual wiring diagram, using all OEM retaining clips to prevent the harness from contacting any metal edges during vehicle vibration.
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.