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 — Seal U

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.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 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: Repeated bending from opening and closing the door causes partial copper wire breakage where the left curtain airbag wiring harness passes through the left front door hinge, A-pillar, or B-pillar routing holes (common failure point 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, internal slip ring wear increases resistance.
  • 4Left curtain airbag assembly fault: Squib internal resistance increased due to aging, moisture ingress, or manufacturing defects.
  • 5SRS ECU detection circuit fault: Faulty components in the corresponding detection channel inside the airbag control unit cause 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
    Preliminary check: Use BYD VDS or Launch X431 to read the DTC freeze frame. Confirm vehicle status and ambient temperature at the time of the fault to 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 interior trim panel. Verify the left curtain airbag white/yellow connector is fully seated. Inspect the terminals for green oxidation or backing out.
  • 5
    Harness continuity test: Disconnect the SRS ECU and left curtain airbag connectors. Use a multimeter to measure harness continuity between them. Carefully inspect the bent section of the harness at the left front door hinge for open circuits or high resistance (<1Ω).
  • 6
    Component replacement verification: If the wiring harness is normal, remove the left curtain airbag and measure the igniter resistance (standard value: 2.0 ± 0.3 Ω). If the resistance is 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, reconnect the battery. Use the diagnostic tool to clear the fault code and perform 'Configuration and Settings'. Perform the SRS system self-check. Confirm the resistance returns to normal and the warning lamp turns 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 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.