AU
B1796

This DTC indicates a short to body ground in the driver-side second-stage seat belt pretensioner deployment circuit — Seal U

Safety System

This DTC indicates a short to body ground in the driver-side second-stage seat belt pretensioner deployment circuit.

The second-stage pretensioner is a pyrotechnic device in the SRS (Supplemental Restraint System).

It operates in series or parallel with the first-stage pretensioner to provide greater seat belt tightening force during a severe collision (high-speed frontal impact).

A short to ground occurs when damaged insulation on the positive wire from the SRS ECU to the pretensioner squib contacts the vehicle body metal, causing circuit resistance to drop abnormally (typically <1Ω).

The SRS ECU detects this abnormal current path, illuminates the airbag warning lamp, and disables the second-stage pretensioner function.

In a severe collision, the driver may lose second-stage protection, increasing the risk of injury.

In extreme cases, the short-circuit current can accidentally trigger the pretensioner, locking the seat belt and requiring costly replacement.

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Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Harness wear under the seat: Long-term repeated fore-and-aft movement of the driver seat adjustment mechanism wears through the floor harness insulation (especially the SRS harness routed under the seat slide rail), causing the copper wire to contact body ground.
  • 2Pretensioner connector water ingress and corrosion: Poor sealing of the pretensioner connector under the B-pillar or seat allows water entry during vehicle wading or interior cleaning, causing internal pins to oxidize and short to ground.
  • 3Pretensioner internal short circuit: The squib inside the second-stage pretensioner shorts directly to the metal housing due to internal coil insulation failure caused by a manufacturing defect or long-term vibration.
  • 4Foreign object piercing the SRS wiring harness: Metal objects (such as coins or screws) left under the seat pierce the SRS wiring harness sheath during seat movement, causing a short to ground.
  • 5Previous collision repair issues: Sharp sheet metal edges cut a wiring harness not secured to standard, or an incompletely seated pretensioner connector causes the terminal to contact the vehicle body.
What To Do
  • 1
    Safety Preparation and Power-Down: Verify the vehicle is in the OFF position. Wear insulated gloves. Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor. For hybrid/pure electric models, perform the high-voltage system power-down procedure first (disconnect the service plug).
  • 2
    Locate the faulty component: Remove the driver's side lower B-pillar trim panel and seat side trim panel to expose the second-stage seat belt pretensioner (usually integrated into the retractor assembly or the base of the B-pillar). Identify the two-wire connector with the yellow protective sleeve.
  • 3
    Disconnect and isolate: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the two pins on the pretensioner side (normal: 1.5-3.0 Ω), and measure the resistance from each pin to body ground. If the resistance from either pin to ground is <1 MΩ, confirm a short to ground.
  • 4
    Section-by-section harness inspection: If the pretensioner resistance is normal, open the corrugated conduit along the SRS harness section by section from the pretensioner to the SRS ECU. Focus on the harness under the seat slide rail, inside the sill trim panel, and at the floor grommet. Inspect for signs of wear, crushing, or corrosion.
  • 5
    Repair or replace: If the wiring harness is damaged, repair it with heat-shrink tubing or tape and re-secure it at a safe distance from the vehicle body. If the pretensioner has an internal short circuit (pin-to-ground continuity), replace the entire seat belt retractor assembly (including the pretensioner). Do not attempt to repair the pyrotechnic device.
  • 6
    System verification: Reconnect all connectors and the battery. Use the BYD VDS diagnostic tool to clear the fault code and run the 'SRS System Self-test' function. Confirm B1796 does not reappear and the airbag warning light turns off. Finally, perform a seat fore-and-aft movement test to confirm no wiring harness interference.
Real-World Cases
BYD DTC AI Analysis

Song MAX seat rail chafed through SRS harness, causing second-stage pretensioner short circuit

✓
2020 Song MAX. Instrument cluster intermittently displayed "Check Airbag System." VDS scan retrieved DTC B1796. Inspection found the floor harness sheath beneath the driver seat rail worn through by shear forces during seat adjustment, exposing two SRS wires. One wire shorted to the seat frame (chassis ground). The harness retaining clip had detached, letting the wiring drop into the seat track. Repaired the damaged harness by insulating each wire individually and sleeving with corrugated tubing, resecured it with zip ties above the seat frame, and fitted a new retaining clip. Fault resolved.
BYD DTC AI Analysis

Tang DM: Corroded B-pillar connector causes intermittent short circuit after water ingress

✓
2021 BYD Tang DM. After wading through floodwater during heavy rain, the airbag warning light stayed on with DTC B1796. Inspection found mud and water inside the second-stage pretensioner connector below the driver's side B-pillar. The pins had oxidised, producing verdigris that caused unstable resistance between the positive terminal and the connector metal housing (ground) — normal when cold, shorting to ground when hot. Cause: wading depth exceeded the sill seal height. Repair: Cleaned the connector thoroughly with electronic cleaner, dried it with compressed air, applied conductive anti-corrosion compound, and installed a new waterproof connector housing. Fault resolved.
BYD DTC AI Analysis

Yuan EV: Unsecured pretensioner wiring harness following accident repair caused short circuit

✓
A 2019 Yuan EV logged DTC B1796 one month after front collision repairs. Records showed the driver's seat belt assembly was replaced after the accident, but the pretensioner harness wasn't routed to factory specs. The seat adjustment mechanism pinched the harness, damaging the insulation and causing a short to body. Fix: Rerouted the wiring per workshop manual standards, secured the SRS harness clear of moving components using OEM retaining clips, repaired the damaged conductors, cleared the DTC and verified.
BYD DTC AI Analysis

Qin Pro pretensioner internal igniter short circuit false positive

✓
2020 Qin Pro, no collision history, but VDS reports B1796 which will not clear. Disconnected the driver's second-stage pretensioner connector: measured infinite resistance to ground on the harness side (normal), but 0.2Ω between the pretensioner (retractor assembly) pins and metal housing. Confirms the internal pyrotechnic device is shorted to the housing. Supplier batch quality issue. Fix: Replace the driver's side seatbelt retractor assembly (part number must match the VIN to ensure correct trigger level), use VDS to perform the 'replacement component coding' procedure to match the new pretensioner to the SRS ECU. 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.