AU
B164B11

This DTC indicates the SRS (Supplemental Restraint System) control unit detected a short to ground in the front passenger seat belt pretensioner ignition circuit — Seal U

Safety System

This DTC indicates the SRS (Supplemental Restraint System) control unit detected a short to ground in the front passenger seat belt pretensioner ignition circuit.

The seat belt pretensioner is a pyrotechnic safety device containing a gas generator and a resistance wire igniter, with a normal operating resistance of approximately 1.5-2.5Ω.

The BYD diagnostic protocol defines the DTC suffix '11' as a short to ground fault.

The SRS module sets this code when it detects pretensioner circuit resistance below the threshold (typically <1.0Ω) or abnormal voltage to ground.

This fault forces the SRS into a degraded mode, disables the front passenger pretensioner, and illuminates the instrument cluster airbag warning lamp.

Because the pretensioner contains pyrotechnics, a short circuit risks accidental deployment or failure during a collision.

Address this highest safety level (Level 3) fault immediately.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1The pretensioner wiring harness insulation under the front passenger seat rail or at the base of the B-pillar wears, ages, or is pinched by the seat adjustment mechanism, causing the wire to directly contact the vehicle body metal frame (ground).
  • 2Pretensioner connector (usually a yellow waterproof plug located beside the seat or in the floor wiring harness): water ingress, bent or corroded pins, or loose terminals contacting nearby grounded components.
  • 3Insulation breakdown on the gas generator resistance wire inside the pretensioner body causes an internal short circuit (usually accompanied by an abnormal resistance drop to <1Ω).
  • 4Poor sealing of the front passenger floor wiring harness connector (such as the SJB connection point) allows water ingress during wading or car washing, causing a short circuit between the power wire and ground.
  • 5Internal fault in the SRS control unit (ACU) ignition drive circuit or damaged monitoring chip causing a false short circuit (confirm after ruling out the wiring harness and components).
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor. Never measure the pretensioner terminals directly with a multimeter in resistance mode to prevent the test current from detonating the device.
  • 2
    Visual inspection: Remove the front passenger seat (leave the wiring harness connected) and the lower B-pillar trim panel. Check the pretensioner wiring harness (wrapped in yellow corrugated conduit) for damage, water stains, or crush marks. Specifically inspect harness wear points within the seat slide rail adjustment range.
  • 3
    Connector diagnosis: Disconnect the pretensioner connector and inspect the pins for oxidation, backing out, or bending. Use a multimeter on the voltage setting to measure the harness-side voltage to ground; the reading must be 0V (if measuring under load, power on the system without triggering deployment). Use the high-resistance setting to measure the harness-side resistance to ground; the reading must be >1MΩ.
  • 4
    Component isolation test: Connect a dedicated SRS simulator resistor (2Ω) to the circuit in place of the pretensioner, then clear the fault code. If the fault code becomes a history code or disappears, the pretensioner has an internal short circuit. Replace the seat belt retractor assembly (the pretensioner is usually not available separately).
  • 5
    Wiring harness repair: If the wiring harness is damaged, cut out the damaged section and solder the connection. Apply three layers of heat-shrink tubing (inner layer with adhesive) for waterproof insulation. Do not use twisted joints or electrical tape. After repair, use an insulation resistance tester (500V range) to test insulation to ground; the resistance must be >10MΩ.
  • 6
    System verification: Restore all connections. Connect power, use VDS or a dedicated diagnostic tool to read the data stream, and confirm the pretensioner resistance is 1.5-2.5Ω. Execute the SRS system self-diagnosis. Confirm B164B11 is cleared and the instrument warning light is off. Perform static and dynamic road tests to verify.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Pretensioner short circuit repair after water ingress in Qin Pro DM

✓
After driving through water approximately 30 cm deep, the instrument panel airbag warning light remained illuminated. Retrieved DTC B164B11 (current fault). Inspected the front passenger carpet and found it heavily saturated. Removed the front passenger seat and discovered water inside the seat belt pretensioner connector (located on the front mounting bracket of the seat rail). Water between the copper pins caused a short to ground. Thoroughly dried the wiring harness and connector using compressed air, cleaned the pin oxides, applied dielectric grease, and reassembled. Resolved the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

E2 EV seat modification caused wiring harness damage

✓
The owner installed full-wrap seat covers. The retaining clip screws pierced the pretensioner harness sheath. Road vibration caused the copper wires to chafe against the seat frame, intermittently setting DTC B164B11. Inspection showed an M6 screw had pierced the harness at the frontmost end of the seat rail, causing two wires to short to earth. We cut out the damaged section, re-soldered the wires, and applied three layers of heat-shrink tubing for waterproofing. We rerouted the harness to clear the seat mechanism. The fault has not returned.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Replaced the Qin EV pretensioner assembly due to abnormal internal resistance.

✓
DTC B164B11 appeared intermittently, frequently on cold starts. Scan tool live data showed passenger-side pretensioner resistance at 0.6 Ω (spec 1.8–2.2 Ω). Diagnosed as internal resistance wire insulation breakdown in the gas generator causing a short to ground. Replaced the passenger-side seat belt retractor assembly (with pretensioner). Performed SRS system configuration using BYD factory scan tool (programmed new component serial number). Executed system self-test and static test. Cleared the DTC.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

B-pillar trim removed and refitted, connector left unplugged, causing short circuit

✓
The vehicle logged fault code B164B11 after the B-pillar trim panel was removed for window tinting. Inspection found the pretensioner connector (at the floor wiring harness junction below the B-pillar) was not fully seated — the locking tab had not engaged, causing the connector to tilt. Internal terminals contacted the B-pillar metal frame, creating a short to ground. Realigned the connector until the locking tab clicked into place, confirmed the waterproof seal was intact, and cleared the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Replaced ACU because SRS control unit reported a false fault.

✓
After replacing the passenger-side pretensioner and wiring harness, DTC B164B11 remained current and could not be cleared. Measured the new pretensioner resistance (2.0Ω), wiring harness insulation resistance to ground (>20MΩ), and verified normal circuit continuity using a multimeter. Determined the fault to be the SRS control unit (ACU) internal ignition monitoring circuit. Replaced the SRS control unit, performed online programming, VIN matching and system configuration. The DTC cleared successfully and the system returned to normal.
Original source ↗
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. Sources: [1]