AU
B1766

DTC B1766 indicates the SRS (Supplemental Restraint System) control unit cannot identify or establish communication with the Right Front Curtain Shield Airbag — Atto 8

Safety System

DTC B1766 indicates the SRS (Supplemental Restraint System) control unit cannot identify or establish communication with the Right Front Curtain Shield Airbag.

This fault constitutes an "airbag not present" condition; the ECU detects no load signal from the airbag module during the system self-check.

This typically indicates an open airbag circuit (infinite resistance).

Potential causes include a disconnected airbag connector, broken wiring harness, internal open circuit in the airbag module, or poor contact at the ECU terminal.

This safety-critical fault prevents the right front curtain airbag from deploying during a collision, severely compromising side-impact protection.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Right front curtain airbag module connector loose, disconnected, or making poor contact (common if not fully seated after A-pillar trim removal and installation)
  • 2Airbag wiring harness open circuit or wear (especially where the harness passes the A-pillar and roof side rail, as vibration or removal/installation breaks the copper core)
  • 3Internal open circuit in the airbag module (airbag igniter open circuit or internal module circuit fault)
  • 4Internal fault or software error in the SRS control unit (ACU) causing a false 'airbag not present' warning.
  • 5Airbag deployed after a collision but not replaced, or the replacement second-hand airbag module is faulty.
What To Do
  • 1
    Step 1: Safety preparation - Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS system and prevent accidental airbag deployment.
  • 2
    Step 2: Visual inspection - Remove the right front A-pillar trim panel and right roof trim panel. Verify the curtain airbag module connector is fully seated, and inspect the wiring harness for damage, crushing, or water stains.
  • 3
    Step 3: Resistance measurement - Disconnect the airbag connector and use a dedicated SRS resistance tester (a multimeter may trigger a fault) to measure the airbag igniter resistance. The normal value is 1.5-3.0 Ω. A reading of ∞ indicates an internal open circuit in the airbag.
  • 4
    Step 4: Wiring harness continuity test - Measure wiring harness continuity between the airbag connector and the SRS ECU. Focus inspection near the A-pillar hinge and roof wiring harness mounting points. Repair any broken wires.
  • 5
    Step 5: Connector inspection - Check the connector terminals for oxidation, backed-out pins, or deformation. Clean or replace the connector.
  • 6
    Step 6: Replacement verification - If the wiring harness is normal, install a known-good right front side curtain airbag module for verification (part numbers must match).
  • 7
    Step 7: System reset - Connect the battery, use the BYD dedicated diagnostic tool to clear the fault code, perform SRS system configuration coding (if replacing the airbag or ECU), and run a system self-check to confirm B1766 does not return.
Real-World Cases
BYD DTC AI Analysis

Song MAX: Loose right front curtain airbag connector causes B1766

✓
A 2019 Song MAX came in with the airbag warning light on. Scanning with VDS2000 showed code B1766 (Right Front Side Curtain Airbag Not Present). Removed the right front A-pillar trim and found the curtain airbag connector had approximately 2mm of gap and wasn't fully seated—likely from previous A-pillar work. Reconnected the connector firmly, confirmed the locking tab engaged, cleared the fault code, and the SRS light went out. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD S6 SRS wiring harness chafing, open circuit (similar to B1766)

✓
The instrument cluster displayed an airbag warning. The scan tool retrieved side airbag-related DTCs. Inspection found the vehicle had been in a side scrape accident that damaged the wiring harness inside the right front A-pillar. Removing the A-pillar trim revealed damaged airbag harness insulation with the copper conductor fractured, causing an open circuit. Repair: Cut out the damaged section, soldered in specialist high-temperature wire (0.5mm² or larger), wrapped the insulation properly, and rerouted the harness to avoid contact with metal edges. Fault resolved.
Original source ↗
BYD DTC AI Analysis

General Motors Curtain Airbag Module Internal Open Circuit Fault Diagnosis

✓
Symptom: Airbag warning light on. Diagnostic scan showed the right front side curtain airbag was missing or had abnormal resistance. Diagnostic process: Disconnected the airbag connector and measured resistance across the airbag terminals. Found infinite resistance (normal is approximately 2Ω), indicating an open circuit in the airbag module internal igniter. Checked continuity of the wiring harness from the airbag to the SRS ECU; it was normal. Connectors showed no abnormalities. Solution: Replaced the right front side curtain airbag module with a new unit (along with the airbag label and SRS ECU configuration update). Cleared the fault codes; the system returned to normal.
Original source ↗
Other Atto 8 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.