AU
B17091A

DTC B17091A indicates the airbag control unit (SRS ECU) detects the resistance of the left-hand curtain shield airbag igniter circuit is below the system calibration threshold (typically below 1 — Qin Plus

Safety System

DTC B17091A indicates the airbag control unit (SRS ECU) detects the resistance of the left-hand curtain shield airbag igniter circuit is below the system calibration threshold (typically below 1.5Ω; standard operating range is 1.5-3.0Ω).

An internal short circuit in the curtain airbag igniter, a wiring harness short to ground, or shorted connector terminals can cause this low-resistance fault in the igniter circuit.

After the SRS system enters fail-safe mode, the left-hand curtain shield airbag may fail to deploy during a side impact, posing a severe safety risk.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Internal short circuit in the left side curtain airbag igniter (airbag module aging, moisture exposure, or mechanical impact damages the internal igniter coil insulation, causing a short circuit)
  • 2Wiring harness short to ground (wiring harness chafing inside the A-pillar, C-pillar, or headliner trim panel damages the insulation, causing a short to the vehicle body)
  • 3Connector fault (water ingress, corrosion, deformed terminals causing a short circuit, or loose terminals causing poor contact in the connector between the SRSECU and the curtain airbag)
  • 4Improper modification or repair (damage to wiring harness insulation when installing a dash cam or roof ambient lighting, or impedance mismatch from non-genuine parts)
  • 5SRS ECU internal detection circuit fault (abnormal internal sampling resistor or A/D conversion circuit in the control unit causes a false low resistance reading)
What To Do
  • 1
    Safety preparation: Turn the ignition switch to OFF, disconnect the negative battery terminal, and wait at least 90 seconds to allow the SRS backup power supply capacitor to fully discharge.
  • 2
    Fault Confirmation: Use the BYD VDS diagnostic tool to read the fault code. Confirm B17091A is a Current DTC rather than a history code. Record the resistance value from the freeze frame data.
  • 3
    Visual inspection: Remove the left A-pillar trim panel and the left edge of the headliner. Inspect the left curtain airbag wiring harness connector (usually located below the A-pillar or at the front of the headliner) for looseness, water ingress, corrosion, or physical damage.
  • 4
    Resistance measurement: With the power off and the SRS ECU connector disconnected, use a digital multimeter to measure the resistance between the two terminals of the left curtain airbag inflator (Normal: 1.5-3.0 Ω; less than 1.5 Ω is abnormal).
  • 5
    Insulation check: Measure the resistance between each terminal of the curtain airbag wiring harness and body ground (must be greater than 1 MΩ) to check for a short to ground. Measure the insulation between the wires to rule out a short between wires.
  • 6
    Swap verification: Disconnect power. Swap the left and right side curtain airbag harness connections. Restore power and read the fault code. If the fault code changes to B170A1A (right side), the original left side curtain airbag unit is faulty.
  • 7
    Fault repair: If the curtain airbag is faulty, replace the left curtain airbag assembly (remove the headlining); if the wiring harness is faulty, repair the damaged wire and rewrap with insulating tape; if the connector is faulty, clean or replace the terminal.
  • 8
    System reset: Reconnect all connectors, reconnect the battery, clear the fault codes, and perform the SRS system self-check cycle (cycle the ignition switch from OFF to ON three times at 5-second intervals).
  • 9
    Final verification: Confirm the SRS warning light turns off normally (6 seconds after power-on). Use the diagnostic tool to confirm no current fault codes exist. Measure the curtain airbag resistance and verify it is within the standard range. Perform static and road tests.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM left curtain airbag wiring shorted after water ingress

✓
2019 BYD Qin Pro DM. After driving through water, the SRS warning light stayed on. Used VDS to retrieve DTC B17091A (left side curtain airbag resistance too low). Removed the left C-pillar trim panel and found obvious water staining and verdigris corrosion inside the wiring harness connector. Resistance between terminals measured only 0.3Ω. Thoroughly cleaned the connector with electronic cleaner, dried it, applied conductive protectant, and reinstalled. After repair, curtain airbag resistance restored to 2.1Ω. After clearing the fault code, system self-test passed.
Original source ↗
BYD DTC AI Analysis

Qin Pro curtain airbag internal short circuit after accident repair

✓
2018 BYD Qin Pro petrol variant. After left side collision repair (curtain airbag did not deploy), the instrument cluster displayed an SRS fault. The diagnostic tool read code B17091A. Measured left curtain airbag resistance at 0.6Ω (far below spec). The impact crushed and deformed the curtain airbag housing, shorting the igniter coil internally. Replaced the left curtain airbag assembly (part number: SC-5859600). Seated the connector clip fully during installation. Retested resistance at 2.2Ω. Fault resolved.
BYD DTC AI Analysis

Aftermarket ambient lighting installation damaged the wiring harness.

✓
Qin Pro DM owner installed roof ambient lighting, triggering the SRS warning light. DTC B17091A indicated abnormal resistance in the left curtain airbag. Inspection found a harness clip used to secure the wiring during the modification had pierced the yellow dedicated wiring harness for the left curtain airbag, causing a short between the supply wire and chassis earth. Repaired the damaged wire using 0.5mm² high-temperature resistant wire, soldered the connections, applied double-layer heat shrink tubing for insulation, rerouted the harness away from sharp components, and cleared the fault.
BYD DTC AI Analysis

Poor connector contact causes intermittent fault.

✓
The SRS warning light would illuminate intermittently, sometimes going out on its own while driving. A diagnostic scanner read intermittent fault code B17091A. Inspection revealed slight oxidation and terminal spread on pins 15 and 16 of the SRS ECU connector (for the left curtain airbag), causing unstable contact resistance that was sometimes too low. Repaired the terminals with a special tool, applied electrical contact protectant, and verified the connector lock was intact. After one month of monitoring, the fault has not recurred.
Other Qin Plus 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.