AU
B1796-00

DTC B1796-00 indicates a short to ground in the control circuit of the driver-side second-stage seat belt pretensioner — Seal U

Safety System

DTC B1796-00 indicates a short to ground in the control circuit of the driver-side second-stage seat belt pretensioner.

The second-stage pretensioner is a dual-stage ignition component of the Supplemental Restraint System (SRS).

During a severe collision, a pyrotechnic device rapidly tightens the seat belt to eliminate slack between the occupant and the belt. "Short to ground" indicates an insulation failure between the pretensioner drive harness (typically the positive control wire) and the vehicle body ground (GND), causing resistance to drop abnormally (<1Ω).

This fault causes the SRS control unit (ACM) to detect abnormal circuit current, trigger fail-safe mode, and disable the pretensioner.

In extreme cases, this prevents the seat belt from tightening properly during a collision or creates a risk of unintended deployment under specific conditions.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness abrasion inside the B-pillar trim panel: As the driver's seat belt pretensioner wiring harness passes beneath the B-pillar, long-term seat adjustment or vibration from door operation causes metal edges to cut the insulation, resulting in a short to ground.
  • 2Corrosion of the connector under the seat: Vehicle wading, improper interior cleaning, or a blocked sunroof drain allows water to flow under the seat. The water oxidizes and electrolytically corrodes the yellow pretensioner connector terminals, creating a short-to-ground path.
  • 3Internal short circuit in the pretensioner body: Moisture in the second-stage igniter pyrotechnic charge or a manufacturing defect causes insulation failure between the ignition wire and the metal housing.
  • 4SRS control unit internal drive circuit fault: ACM internal ignition drive chip breakdown causes the output terminal to short to ground, triggering a false pretensioner fault.
  • 5Improper modification or accident repair: During seat heater installation, racing seat modification, or accident repair, removing and installing the seat belt assembly pinches the wiring harness or detaches retaining clips, causing the wiring harness to contact the vehicle body metal.
What To Do
  • 1
    Safe power-down: Turn off the ignition, disconnect the negative battery terminal, and wait at least 3 minutes to fully discharge the SRS system capacitor and prevent accidental pretensioner deployment.
  • 2
    Visual inspection: Remove the driver-side B-pillar lower trim panel and under-seat protective panel. Check the pretensioner wiring harness (yellow corrugated conduit) for wear, cuts, or burn marks. Focus on contact points between the wiring harness and body sheet metal.
  • 3
    Connector diagnosis: Disconnect the pretensioner connector (usually located under the seat or at the base of the B-pillar). Inspect the terminals for green oxidation, water stains, or burn marks. Clean with compressed air and apply electronic contact protectant if necessary.
  • 4
    Resistance measurement: Use a multimeter to measure the pretensioner body resistance (connector side). The normal value is 1.8-3.2 Ω. Measure the insulation resistance to ground on the wiring harness side; it must be greater than 1 MΩ. Resistance <1 Ω indicates a short circuit.
  • 5
    Wiring harness repair: If the wiring harness is damaged, strip the insulation, repair the wire with solder, apply double-layer heat-shrink tubing for insulation, and re-secure the wiring harness routing. Maintain a clearance of at least 20mm from the body.
  • 6
    Component replacement: If the pretensioner has an internal short circuit (abnormal resistance and normal wiring harness), replace the driver-side seat belt assembly (including the pretensioner). Note: The pretensioner is an explosive component. Handle the old part according to dangerous goods transport regulations.
  • 7
    System reset: Connect the battery, use the diagnostic tool to clear the fault code, and perform 'SRS System Configuration' or 'ECU Re-coding' (if replacing the control unit). Finally, perform an ignition switch cycle test to confirm the fault code does not recur.
Real-World Cases
BYD DTC AI Analysis

B-pillar wiring harness chafing caused intermittent short circuit on Qin EV300

✓
**Symptoms:** Airbag warning light comes on intermittently on rough roads, goes off on smooth surfaces. Intermittent DTC B1796-00. Owner reported recent seat height adjustment. **Diagnosis:** Removed B-pillar lower trim panel. Found driver seatbelt pretensioner harness (yellow) had chafed through insulation at seat rail mounting bracket, with copper conductor contacting chassis ground. Resistance fluctuated between 0.2Ω and 5Ω during vehicle vibration. **Resolution:** Repaired damaged harness (soldered, double-layer heat shrink tubing), adjusted harness routing and added rubber protective sleeve, re-secured to harness bracket. Fault resolved.
BYD DTC AI Analysis

Qin 100 pretensioner connector corroded after water ingress

✓
**Symptoms:** After driving through deep water, the airbag warning light remained on constantly. Scanned DTC B1796-00. Found the carpet under the driver's seat was wet. **Diagnosis:** Removed the seat. The pretensioner connector (yellow 2-pin) had obvious water stains and green corrosion inside, with insulation resistance between terminals down to 0.8Ω. The sunroof drain tube had detached, allowing rainwater to run down the A-pillar and pool beneath the seat. **Resolution:** Thoroughly dried the seat and wiring harness. Cleaned the connector terminals with precision instrument cleaner, blew them dry, then applied dielectric grease. Repaired the drain tube. Cleared the fault code; it did not return.
BYD DTC AI Analysis

Qin EV450 second-stage pretensioner internal short circuit

✓
**Symptoms:** No collision history. Airbag warning light stays on after normal startup. DTC B1796-00 stored and will not clear. **Diagnosis:** Disconnected the pretensioner plug under the seat. Measured >10MΩ insulation to earth on the harness side (normal). Measured 0.3Ω across the pretensioner itself (specification ~2.0Ω). Determined the second-stage igniter has an internal short to housing. **Repair:** Replaced the driver-side seat belt assembly (Part No. BYD-5820XXXX). Post-repair resistance measured 2.1Ω. Cleared the DTC; system self-test passed. Processed the old component per explosive material recycling procedure.
BYD DTC AI Analysis

Seat modification pinched the pretensioner harness, causing a short circuit.

✓
**Symptoms:** After installing racing seats, the airbag warning light came on while driving with DTC B1796-00. The shop had removed the factory seatbelt buckles. **Diagnosis:** The aftermarket seat bracket was crushing the factory pretensioner wiring harness, damaging the insulation and shorting it to the bracket (chassis ground). Resistance at the short: 0.1Ω. **Resolution:** Removed the aftermarket seats and repaired the harness (cut and re-spliced due to severe damage). Re-routed the wiring to clear the seat rail travel path and added a harness protection plate. Fault cleared. Advised the owner to use pretensioner-compatible seats or retain the factory seatbelt system for any future modifications.
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.