AU
B173A1A

DTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω — Atto 3

Safety System

DTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω.

In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω.

A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit.

This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Airbag module internal igniter short circuit: Manufacturing defects, aging, or previous electrostatic discharge cause the igniter resistance wire to blow or short-circuit.
  • 2Seat wiring harness mechanical damage: The right middle-row side airbag wiring harness typically routes through the seat frame or moves during seat adjustment. Prolonged friction damages the insulation, causing the core wire to short to ground.
  • 3Connector fault: Terminals inside the yellow dedicated airbag connector are bent or backed out, or water or cleaning fluid ingress causes a short circuit between the pins.
  • 4SRS control unit internal fault: Damaged ACU internal detection circuit falsely reports a short circuit fault (rule out external wiring before confirming).
  • 5Improper modification or repair: failing to secure the wiring harness during seat removal and installation, or piercing the airbag wiring harness when installing seat covers.
What To Do
  • 1
    Safe power-down: Switch off the ignition, disconnect the 12V battery negative terminal, and wait at least 90 seconds for the SRS capacitor to fully discharge.
  • 2
    Fault confirmation: Use the dedicated diagnostic tool to read freeze frame data, record vehicle status at the time of the fault, and confirm whether the fault is current or history.
  • 3
    Disconnect and measure: Remove the right middle row seat side trim panel. Locate and disconnect the yellow airbag connector. Use a digital multimeter to measure the resistance at the airbag module side (normal: 2-5 Ω; if 0 Ω, replace the airbag module).
  • 4
    Harness continuity test: Measure resistance to ground on the harness side (should be >1MΩ). Inspect the harness for wear at the seat rails and hinges, focusing on the flexible harness section that moves with the seat.
  • 5
    Connector inspection: Check terminals for bending or corrosion. Measure for short circuits between connector terminals. Clean or replace the connector if necessary.
  • 6
    Repair verification: After repairing or replacing the faulty component, reconnect all connectors and the battery, use the diagnostic tool to clear the fault code, and perform a 'system self-check' (complete 3 ignition cycles).
  • 7
    Final confirmation: Confirm the SRS warning lamp turns off. Use the diagnostic tool to read the data stream and confirm the airbag resistance value has returned to the normal range.
Real-World Cases
BYD DTC AI Analysis

Worn seat rails caused a wiring harness short circuit.

✓
Vehicle: 2019 Qin EV Symptom: SRS light always on, fault code B173A1A. Diagnosis: Removed right second-row seat. Found side airbag harness clip had detached from the seat fore-aft adjustment rail. The rail trapped the harness, chafed through the insulation, and caused a short to earth. Measured resistance to earth: 0.3 ohms. Solution: Replaced damaged harness section. Rerouted and secured the harness, then added abrasion-resistant sleeving. Fault cleared.
BYD DTC AI Analysis

Corrosion in airbag connector due to water ingress

✓
Model: E3 2020. Symptoms: SRS warning light on after wading through water, storing DTC B173A1A. Diagnosis: Inspected the right middle-row side airbag connector (under the seat) and found obvious water stains and verdigris corrosion inside. Decreased insulation resistance between terminals caused a short circuit. Water level likely exceeded the floor wiring harness height when the vehicle waded through water. Resolution: Replaced the airbag harness connector (including terminals), cleaned the airbag module pins, and dried the entire vehicle wiring harness. Fault cleared.
BYD DTC AI Analysis

Airbag module internal igniter fault

✓
Model: E2 2019. Symptoms: After accident repairs and replacement of the airbag, the SRS warning light remained illuminated with DTC B173A1A. Diagnosis: Disconnected the airbag module connector and measured 0Ω across the module terminals (normal reading is 2-3Ω), confirming the new aftermarket airbag module had a manufacturing defect in the internal igniter causing a short circuit. Testing on the wiring harness side showed normal resistance (infinite to ground). Fix: Replaced the genuine right middle row side airbag module, recoded the system, and restored normal operation.
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.