AU
B170A-00

DTC B170A-00 indicates the Supplemental Restraint System (SRS) detected the resistance in the left curtain shield airbag igniter circuit exceeds the calibrated threshold (normal range is typically 2 — Atto 8

Safety System

DTC B170A-00 indicates the Supplemental Restraint System (SRS) detected the resistance in the left curtain shield airbag igniter circuit exceeds the calibrated threshold (normal range is typically 2.0-3.0Ω; fault threshold is generally >3.5Ω or open circuit).

The SRS ECU continuously monitors the circuit impedance of each airbag igniter using a low-current detection circuit.

Excessive resistance indicates a high-resistance condition in the circuit.

Potential causes include poor connector contact, a partially broken wiring harness, or increased internal resistance from igniter aging.

This fault prevents the left curtain shield airbag from deploying normally during a collision and constitutes a critical failure in the passive safety system.

The B170A-00 fault code on the Atto 8 indicates the SRS has detected excessive resistance or an open circuit in the left curtain airbag igniter circuit. This is a medium-severity safety issue because the airbag may not deploy correctly in a crash. Common causes include a loose or oxidized connector, or damaged wiring near the pillar or door hinge area. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Loose or oxidized left curtain airbag igniter connector: Moisture or vibration increases contact resistance at the connector located inside the left C-pillar trim panel or on the left roof side rail.
  • 2Wiring harness wear or breakage: Long-term bending from opening and closing the door partially breaks the copper wires where the left curtain airbag harness passes through the left front door hinge, A-pillar, or B-pillar routing holes (common failure area on Qin series models).
  • 3Clock spring (spiral cable) internal fault: If the vehicle's steering wheel-to-body wiring harness includes the curtain airbag circuit, wear on the clock spring's internal slip ring increases resistance.
  • 4Left curtain airbag unit fault: Increased squib internal resistance due to aging, moisture ingress, or manufacturing defects.
  • 5SRS ECU detection circuit fault: A faulty component in the corresponding detection channel inside the airbag control unit causes a false high resistance reading.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal. Wait at least 90 seconds to fully discharge the SRS backup power supply and prevent accidental airbag deployment.
  • 2
    Initial inspection: Use BYD VDS or Launch X431 to read the DTC freeze frame, confirm vehicle status and ambient temperature at the time of the fault, and rule out intermittent interference.
  • 3
    Data stream analysis: Access the SRS system data stream and check the 'left curtain airbag resistance' value (normal: approx. 2.5Ω; a reading >4Ω or 'open circuit' confirms the fault).
  • 4
    Connector check: Remove the left C-pillar trim panel and left roof trim panel. Verify the left curtain airbag white/yellow connector is fully seated. Inspect the terminals for green oxidation or push-out.
  • 5
    Harness continuity test: Disconnect the SRS ECU and left curtain airbag connectors. Use a multimeter to measure harness continuity between them. Inspect the bent section of the harness at the left front door hinge for an open circuit or high resistance (should be <1Ω).
  • 6
    Component replacement verification: If the wiring harness is normal, remove the left curtain airbag and measure its igniter resistance (standard value: 2.0 ± 0.3 Ω). If the resistance is too high, replace the left curtain airbag assembly. If the curtain airbag is normal but the fault persists, check or replace the SRS ECU.
  • 7
    System reset: After repair, connect the battery. Use the diagnostic tool to clear the fault code and perform 'Configuration and Settings'. Perform the SRS system self-check and confirm the resistance returns to normal and the warning light is off.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 left curtain airbag connector oxidised, causing high resistance

✓
A 2018 Qin EV450 with 30,000 km showed a constant SRS warning light. Scanned with VDS, retrieved DTC B170A-00 (left side curtain airbag resistance too high). Data stream showed resistance at 5.8Ω (out of spec). Removed the left C-pillar trim and found obvious green oxidation inside the left roof curtain airbag connector — caused by moisture ingress from a previous window tint installation. Cleaned the pins with electronic contact cleaner, applied conductive grease, and reconnected the connector. Resistance returned to 2.4Ω. Fault cleared.
BYD DTC AI Analysis

Qin 100 left front door hinge wiring harness worn through and broken.

✓
2017 BYD Qin 100 had B170A-00 DTC. Left side curtain airbag resistance showed 'open circuit'. Inspection found wiring harness insulation worn through at the left front door hinge (below A-pillar) from repeated door opening/closing, with internal copper conductors fractured down to only 2-3 strands remaining, creating high resistance. After stripping back the harness and locating the break, the copper cores were spliced using a dedicated crimping pliers, soldered, and sealed with heat-shrink tubing. The wiring was rerouted and additional anti-chafe sleeving added. Fault resolved. This is a common issue on Qin series vehicles.
BYD DTC AI Analysis

Replaced the aged curtain airbag igniter on the Qin EV300

✓
A 2017 Qin EV300 developed DTC B170A-00 following accident repairs. Wiring harness continuity tested normal. Direct measurement of the left curtain airbag showed a resistance of 8.5Ω, severely out of specification. Diagnosis determined the curtain airbag's internal igniter had sustained impact damage during the collision or had aged, causing increased internal resistance. Replaced the left curtain airbag assembly (part number: ...). Used VDS to perform ECU configuration coding, which requires entering the resistance value parameter from the new airbag label. Performed a system self-test, and the fault code cleared.
BYD DTC AI Analysis

Resolved false SRS ECU fault with software update

✓
Multiple 2017 BYD Qin 80s simultaneously set DTC B170A-00 and similar resistance-related fault codes. Measured the actual wiring resistance and curtain airbag resistance; both were within normal range. A BYD Technical Service Bulletin (TSB) confirmed that early batch SRS control unit software calibration was overly sensitive, causing false DTCs. Upgraded the SRS ECU software via VDS from V1.2 to V1.4. The fault codes cleared after the update and system monitoring returned to normal.
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.