AU
B17281B

DTC B17281B indicates the Supplemental Restraint System (SRS) detects the right knee airbag (front passenger knee airbag) igniter circuit resistance exceeds the normal threshold (typically >3 — Seal U

Safety System

DTC B17281B indicates the Supplemental Restraint System (SRS) detects the right knee airbag (front passenger knee airbag) igniter circuit resistance exceeds the normal threshold (typically >3.5Ω; normal range 1.5-3.0Ω).

This open-circuit fault indicates high resistance or an open circuit in the airbag igniter circuit.

When the SRS control module detects continuously high resistance, it flags the airbag as abnormal, illuminates the airbag warning light, and disables deployment of the affected airbag.

During a collision, the right knee airbag may fail to deploy, disabling lower limb and pelvic protection for the front passenger and increasing the risk of injury.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose knee airbag module connector, backed-out terminals, or oxidized terminals: Located under the front passenger dashboard; cabin humidity or vibration increases contact resistance.
  • 2Airbag igniter internal open circuit or aging: A broken igniter bridge wire or oxidized resistance wire inside the airbag module causes increased resistance.
  • 3Wiring harness open circuit or localized damage: Poor contact, breakage, or moisture corrosion in the wiring harness from the SRS ECU to the right knee airbag, inside the instrument panel or at the floor harness connection point.
  • 4SRS control module internal sampling circuit fault: ECU internal resistance detection circuit malfunction falsely detects a normal resistance value as too high.
  • 5Improper reassembly after repair: Connector not fully locked or keyed retaining clip not seated after replacing the instrument panel assembly or knee airbag.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the DTC freeze frame data. Confirm the DTC status is Active, note the specific resistance value, and record the environmental data.
  • 2
    Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 3
    Remove the front passenger side lower dashboard trim panel and locate the right knee airbag module (usually below the glove box). Check if the airbag connector (yellow marking) is fully locked, and inspect the terminals for oxidation, backed-out pins, or signs of water ingress.
  • 4
    Use a dedicated airbag tester or a simulator resistor (2Ω) in place of the airbag module. Measure the circuit loop resistance to determine whether the fault is on the wiring harness side or the airbag module side. Never measure the airbag igniter directly with a standard multimeter.
  • 5
    Disconnect the SRS control module connector and measure wiring harness continuity from the ECU to the airbag connector. Inspect the transfer connector between the instrument panel wiring harness and the floor wiring harness (usually located in the middle of the center console or below the A-pillar) for oxidation.
  • 6
    If the wiring harness is normal, replace the right knee airbag module (install new retaining clips simultaneously). If the wiring harness is faulty, repair the wiring harness and apply waterproof insulation.
  • 7
    Reconnect all connectors and the battery, clear the fault codes, and perform an SRS system self-check (turn the ignition switch to ON and verify the airbag warning lamp turns off after 6 seconds). Finally, perform a crash simulation test (use the diagnostic tool to run the actuator test function to verify circuit integrity).
Real-World Cases
BYD DTC AI Analysis

Qin PRO DM: High resistance in right knee airbag after water wading

✓
A 2019 BYD Qin Pro DM owner reported the airbag warning light stayed on after driving in heavy rain. Retrieved DTC B17281B. Inspection found the front passenger carpet wet. Removing the right knee airbag revealed water in the connector and green oxidation on the terminals. Water entered behind the dashboard through the air conditioning intake while driving through water. The repair: cleaned and dried the wiring harness connector, replaced the right knee airbag module (as the internal igniter may have become damp), and applied dielectric grease to the connector. Fault resolved.
BYD DTC AI Analysis

Replaced instrument panel on Qin Pro, airbag warning light now on.

✓
2018 Qin Pro petrol variant. The day after a dealership replaced the instrument panel assembly, DTC B17281B appeared. Inspection revealed the technician hadn't fully seated the right knee airbag harness connector during installation—they pushed it all the way in but didn't hear it click, resulting in poor terminal contact. Fix: disconnected and reconnected the connector, confirming it locked into place (audible click). Cleared the fault codes and the resistance returned to 2.1 Ω. Problem solved.
BYD DTC AI Analysis

Intermittent high resistance after driving on rough roads

✓
A 2019 BYD Qin Pro DM had an intermittent airbag warning light on rough roads, normal on smooth roads. Diagnosis found an intermittent DTC; circuit resistance fluctuated between 2.8–4.2 Ω. Inspection revealed the right knee airbag wiring harness rubbing against the metal dashboard bracket. Prolonged friction wore through the insulation and partially fractured the copper wires, causing an intermittent connection. Repaired the harness, re-wrapped and rerouted it clear of the sharp bracket, and secured it with cable ties to prevent movement. Fault eliminated.
BYD DTC AI Analysis

SRS control module falsely reporting high resistance

✓
A 2018 Qin Pro had multiple right knee airbag resistance measurements all within normal range (2.0 Ω), but the diagnostic tool kept logging DTC B17281B and displaying a 5.2 Ω reading. Inspected wiring harness and found no faults. Suspected internal sampling circuit fault in the SRS control module. Substituted a known-good SRS module — fault code cleared. Repair: Replaced airbag control module (reprogramming required to match VIN and configuration). Fault resolved.
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.