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 — Seal U

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 — Seal U
  • 1Internal short circuit in the airbag module igniter: Manufacturing defects, aging, or previous electrostatic discharge caused the igniter resistance wire to blow or short-circuit.
  • 2Seat wiring harness mechanical damage: The right second-row side airbag wiring harness routes through the seat frame or moves during seat adjustment. Continuous friction damages the insulation layer, causing the core wire to short to ground.
  • 3Connector fault: Bent or backed-out internal terminals in the yellow dedicated airbag connector, or a short circuit between pins caused by wading or cleaning fluid ingress.
  • 4SRS control unit internal fault: The ACU internal detection circuit is damaged and falsely reports a short circuit fault (confirm after ruling out external wiring).
  • 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: Turn 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 when the fault occurred, and confirm whether it is a current or history fault.
  • 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 harness-side resistance to ground (should be >1MΩ). Inspect the harness for wear at seat rails and hinges. Focus on flexible harness sections that move with the seat.
  • 5
    Connector check: Check terminals for bending or corrosion, and measure for short circuits between connector terminals. Clean or replace the connector if necessary.
  • 6
    Repair verification: After repairing or replacing the faulty part, 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 returns to the normal range.
Real-World Cases
BYD DTC AI Analysis

Worn seat rails caused a wiring harness short circuit.

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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

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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

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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 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.