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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 — Atto 3

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.

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Cases Logged
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.

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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.

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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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.