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B17871B

This DTC indicates an open circuit or high resistance fault in the second-stage firing circuit of the driver-side dual-stage airbag — Atto 3

Safety System

This DTC indicates an open circuit or high resistance fault in the second-stage firing circuit of the driver-side dual-stage airbag.

In modern passive safety systems, a dual-stage airbag inflates in stages according to collision severity: the first stage provides basic cushioning, and the second stage adds inflation during a severe collision to optimize protection.

The "1B" sub-code typically indicates the SRS control module detects second-stage trigger circuit resistance outside the calibrated range (normal: 1.5-3.0 Ω).

Possible causes include a disconnected connector, a wiring harness open circuit, an internal open circuit in the clock spring (spiral cable), or a faulty airbag module.

During a high-speed frontal collision, this fault causes the airbag to deploy in single-stage mode only.

This reduces head and chest protection but typically does not affect normal first-stage airbag operation.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Airbag connector not reseated after recall repair

✓
The vehicle arrived with the airbag light on. Found DTC B17871B. The owner reported an airbag recall was performed at another shop one week earlier. Removed the steering wheel and found the new driver airbag second-stage connector (yellow) was not fully seated and the locking tab had not engaged. Reseated the connector and confirmed the lock engaged. Cleared the fault code; it did not return. Suspected cause: previous technician did not verify connector lock status per standard procedure.
BYD DTC AI Analysis

Clock spring internal fracture causing intermittent fault

✓
The BYD Qin EV owner reported the airbag warning light illuminated intermittently, particularly going out after turning the steering wheel. The scan tool stored history fault code B17871B. Removing the combination switch assembly revealed the clock spring (spiral cable) internal second-stage circuit opened after approximately two turns. Replacing the clock spring assembly and calibrating the steering wheel angle sensor cleared the fault. Prolonged stationary steering caused fatigue fracture of the internal flat cable.
BYD DTC AI Analysis

Steering column wiring harness protective sleeve chafed through, short circuit

✓
E2 showed intermittent airbag warning light flashing on rough roads; static tests normal. Removed and inspected steering column lower harness. Found airbag harness insulation worn through at universal joint mounting bracket from rubbing, second-stage circuit wire nearly severed with unstable contact resistance. Repaired harness (soldered connections with heat-shrink insulation), rerouted and secured harness, added anti-chafe sleeve. Fault resolved.
BYD DTC AI Analysis

Water ingress corroded the airbag connector.

✓
Vehicle drove through water exceeding the door sill height. Two weeks later the airbag warning light illuminated with DTC B17871B. The connector below the driver's airbag (inside the lower steering wheel trim panel) showed water staining and green corrosion. Oxidised pins caused contact resistance >5Ω. Cleaned the pins, sprayed electronic contact cleaner, applied conductive grease, and reconnected the connector. Fault cleared. Check the door seals and drain holes.
BYD DTC AI Analysis

Airbag module coding error after accident repair

✓
Fitting a used airbag module to a repaired accident vehicle set DTC B17871B. The replacement module did not match the vehicle configuration—a single-stage unit was installed in a dual-stage system. The E2 base model uses single-stage airbags, while the high-spec variant uses dual-stage units; the incorrect module meant the SRS ECU could not recognise the second-stage circuit. Replacing the driver airbag assembly with the correct part number cleared the fault and the system passed its self-check.
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.