AU
B1793-00

DTC B1793-00 indicates the Driver 2nd Stage Seat Belt Pretensioner circuit resistance exceeds the normal threshold set by the SRS ECU (typically >3 — Seal U

Safety System

DTC B1793-00 indicates the Driver 2nd Stage Seat Belt Pretensioner circuit resistance exceeds the normal threshold set by the SRS ECU (typically >3.6Ω, standard value approx. 2.0Ω ± 0.4Ω).

In the BYD dual-stage airbag system, the seat belt pretensioner uses a staged ignition design: minor collisions trigger the first stage, and severe collisions activate the second stage to provide additional tightening force.

This fault indicates the ECU detected a high-resistance condition in the second-stage squib circuit, likely resulting from poor contact, wiring harness oxidation, or an internal pretensioner open circuit.

This fault disables the second-stage pretensioning function, preventing optimal seat belt restraint during severe collisions and increasing the risk of occupant forward movement.

Additionally, the fault continuously illuminates the SRS warning light and forces the system into a degraded protection mode.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Pretensioner connector under the driver's seat (yellow plug) is loose, oxidized, or has insufficient terminal contact pressure, resulting in increased contact resistance.
  • 2Frequent fore-and-aft seat adjustment wears or pinches the wiring harness beneath the seat frame, causing partial breakage of the internal copper wires or an intermittent connection.
  • 3Seat belt pretensioner internal squib aging, moisture ingress, or manufacturing defects causing resistance drift.
  • 4Vehicle wading or a high-humidity environment causes water ingress and corrosion at the pretensioner connector, forming an oxide layer that increases resistance.
  • 5Pretensioner connector not fully seated after accident repairs, or use of a non-standard substitute resistor during repairs.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal. Wait at least 3 minutes for the SRS capacitor to fully discharge to prevent accidental airbag deployment.
  • 2
    Visual inspection: Verify the yellow pretensioner connector under the driver's seat is fully locked. Inspect the terminals for green oxidation, burn marks, or terminal back-out.
  • 3
    Resistance measurement: Disconnect the connector and use a digital multimeter to measure the resistance between the pretensioner-side terminals. Normal resistance is 2.0Ω±0.4Ω. If the resistance is >3.6Ω, the pretensioner assembly is faulty.
  • 4
    Harness continuity test: Measure harness continuity between the SRS ECU and the pretensioner. Focus inspection on the harness near the seat rail mounting points for breaks or abrasion. Resistance must be <1Ω.
  • 5
    Connector handling: If oxidized, clean the terminals with electrical contact cleaner, apply conductive grease, and replace the connector terminals or wiring harness assembly if necessary.
  • 6
    Component replacement: If pretensioner body resistance is abnormal, replace the driver-side seat belt assembly as a complete unit (including the pretensioner). Do not replace the squib separately.
  • 7
    System reset: Reconnect all connectors and turn on the power. Clear the fault code using the BYD dedicated diagnostic tool. Perform the 'SRS System Configuration and Calibration' procedure. Verify the warning lamp turns off and the resistance reading returns to normal.
Real-World Cases
BYD DTC AI Analysis

Seat adjustment caused intermittent wiring harness connection

✓
Qin EV450, 80,000 km. Owner reported the SRS light occasionally coming on and going out after bumps. Scanned DTC B1793-00; live data showed second-stage pretensioner resistance fluctuating between 2.8–5.2 Ω. Inspection found the pretensioner wiring harness beneath the seat had internal damage at the mounting clip from long-term friction—three copper strands had broken, leaving only two connected, creating high resistance. Repaired the harness and rerouted/resecured the wiring. Resistance stabilized at 1.9 Ω; fault cleared.
BYD DTC AI Analysis

Connector oxidised after water ingress

✓
A BYD Qin 100 that had been driven through heavy flooding showed a constant SRS light with DTC B1793-00. Inspection found water stains and copper oxide inside the pretensioner connector under the driver's seat; terminal contact resistance measured 12Ω. Water had entered the plug through the carpet during the flooding. Cleaned the terminals with WD-40 precision electrical contact cleaner, blew them dry, and applied conductive protective grease. Resistance returned to 2.1Ω. Cleared the fault code and it did not return.
BYD DTC AI Analysis

Connector not locked after accident repair

✓
Accident-repaired BYD Qin 80 kept logging DTC B1793-00 after airbag replacement. Found the driver’s seatbelt second-stage pretensioner connector had been seated but not locked during replacement—no audible click. Road vibration backed the plug out, creating high resistance. Reseated the connector until the lock tab clicked; fault cleared immediately.
BYD DTC AI Analysis

Seatbelt pretensioner internal squib aging

✓
A 5-year-old Qin EV300 with no accident history showed DTC B1793-00. Resistance between the pretensioner connector terminals measured infinite (open circuit); wiring harness continuity tested normal. Diagnosed as an open circuit in the pretensioner's internal second-stage igniter (manufacturing defect or long-term high-temperature aging). Replaced the driver's side seatbelt assembly; resistance measured 2.0Ω and the system passed self-test.
BYD DTC AI Analysis

Aftermarket seat damaged wiring harness

✓
A Qin 100 developed DTC B1793-00 after receiving aftermarket electric seats. The workshop found the modification shop had pinched the pre-tensioner harness between the seat frame and slide rail during installation, damaging the insulation and partially severing the copper strands so they intermittently shorted to the body. The harness was repaired and rerouted clear of moving parts, clearing the fault.
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.