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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) — Atto 8

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 Atto 8 indicates a high-severity SRS airbag fault: a short to ground in the driver-side knee airbag ignition circuit. This can stop the airbag deploying correctly or, rarely, cause unintended deployment, so the SRS warning light may stay on. Common causes include damaged wiring insulation or water/corrosion in the connector. Visit an authorised BYD dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Damaged knee airbag wiring harness insulation: Long-term friction or compression (such as driver knee impacts or improper aftermarket pedal installation) damages the wiring harness below the steering wheel or inside the instrument panel, tearing the outer sheath and allowing the copper wire to contact the vehicle body metal.
  • 2Connector water ingress or corrosion: During vehicle wading, A/C condensate leakage, or car washing, water enters the knee airbag connector (usually located under the left side of the dashboard), causing a terminal-to-terminal or terminal-to-housing short circuit.
  • 3Airbag Control Unit (ACU) internal fault: A damaged ACU internal driver circuit or monitoring circuit causes a false short-to-ground fault (actual wiring is normal).
  • 4Internal short circuit in the knee airbag assembly: Internal short circuit in the airbag igniter (very rare; typically causes abnormally low airbag resistance).
  • 5Improper repair operations: Screws crushed or clips pierced the wiring harness during previous removal of the instrument panel or knee bolster, or improper securing during reassembly allowed 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 bolster (Under Cover). Inspect the knee airbag wiring harness (yellow sleeve marking) for crushing, cuts, or abrasion. Focus on contact points with the steering column and metal brackets.
  • 3
    Connector check: Disconnect the knee airbag connector (usually protected by a shorting bar/shorting spring). Inspect the terminals for signs of 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. Normal resistance is infinite (OL). A resistance of less than 1Ω indicates a short circuit.
  • 4
    Wiring harness insulation test: Use a megohmmeter or a multimeter on the high-resistance setting to measure the insulation resistance to ground of the knee airbag circuit (from the airbag connector to the ACU connector). The resistance must be greater than 10MΩ.
  • 5
    Airbag unit test: After confirming normal wiring, measure the resistance between the two terminals of the knee airbag assembly (typical standard value: 2.0-3.0 Ω). Measure the resistance between each terminal and the airbag metal housing (standard value: infinite). If any terminal has continuity to the housing, replace the airbag assembly.
  • 6
    Fault repair: Replace the damaged wiring harness or repair the insulation (seal tightly using heat-shrink tubing). Clean or replace corroded connectors. Fully seat the wiring harness retaining clips 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 includes cycling the ignition switch). Confirm B1718 does not return and the airbag warning light is 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 Atto 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.