AU
B1792-00

This fault code indicates the driver-side second stage seat belt pretensioner ignition circuit resistance falls below the normal threshold set by the SRS control unit (ACU) (typically 2 — Qin Plus

Safety System

This fault code indicates the driver-side second stage seat belt pretensioner ignition circuit resistance falls below the normal threshold set by the SRS control unit (ACU) (typically 2.0-4.0Ω; actual detected value below 1.5Ω or close to 0Ω).

The second stage pretensioner is part of the dual-stage gas generator system, providing progressive restraint force during a severe collision.

Low resistance typically indicates an internal squib short circuit, a wiring harness short to ground, or internal connector bridging.

This fault causes the ACU to disable the pretensioner function.

In extreme cases, the pretensioner may fail to deploy during a collision, or false fault detection during driving may continuously illuminate the SRS warning light, compromising the overall occupant restraint system protection strategy.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Pretensioner squib internal short circuit: Prolonged exposure to heat and humidity, manufacturing defects, or chemical corrosion causes the igniter charge to absorb moisture, reducing the insulation resistance between the two terminals.
  • 2Wiring harness connector fault: Water ingress into the connector under the driver's seat or near the B-pillar, bent/backed-out pins, terminal bridging, or corrosion causing the signal wire to short to ground or power.
  • 3Mechanical damage: Repeated friction from the seat rail adjustment mechanism, improper seat removal and installation, or foreign objects pinching the harness damages the pretensioner wiring harness insulation, causing a short to ground.
  • 4Seat belt retractor assembly fault: Internal short circuit in the pretensioner body, or contact between retractor metal components and the ignition terminal creates a low-resistance path.
  • 5ACU detection circuit misjudgment: A fault in the airbag control unit internal sampling resistor or A/D conversion circuit causes the unit to misread normal resistance values (less common, but requires inspection).
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 3 minutes to fully discharge the SRS backup power supply and prevent accidental airbag deployment.
  • 2
    Initial diagnosis: Use the BYD VDS or Launch X431 to read all DTCs and freeze frame data. Confirm if B1792-00 is a current or history code, and check for other SRS-related fault codes.
  • 3
    Circuit isolation: Remove the driver-side B-pillar trim and locate the seat belt pretensioner connector (usually a yellow waterproof plug). Disconnect the connector to isolate the pretensioner from the wiring harness.
  • 4
    Resistance measurement: Use a digital multimeter (low current range, <1mA) to measure the resistance directly across the pretensioner body terminals. The standard value is 2.0-4.0 Ω. A reading below 1.5 Ω or close to 0 Ω indicates a short circuit in the pretensioner body. Replace the seat belt retractor assembly.
  • 5
    Wiring harness inspection: Measure resistance between the harness-side connector terminals and ground (should be >10MΩ) and resistance between terminals (should be open circuit). Check for shorts to ground or shorts between wires. Inspect the harness insulation near the seat rails for wear.
  • 6
    Connector inspection: Inspect the connector pins for back-out, bending, or green corrosion. Clean with electrical contact cleaner and verify the locking tab is intact. If the connector shows signs of water ingress, identify the source (e.g., poor window sealing).
  • 7
    ACU verification: If the pretensioner and wiring harness are normal, check the ACU connector pins for oxidation and measure continuity from the ACU to the pretensioner. If necessary, use an oscilloscope to check the ACU detection pulse waveform.
  • 8
    Repair verification: After replacing the faulty component, reconnect all connectors, restore battery power, clear the fault code, and perform an SRS system self-check cycle (ignition switch ON-OFF three times). Verify the fault code does not return and the SRS warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 pretensioner shorted after driving through water

✓
A 2017 BYD Qin EV300 came in with the SRS warning light on after driving through flood water. Retrieved DTC B1792-00. Found water in the wiring harness connector beneath the driver's seat; resistance between the pretensioner terminals measured 0.8Ω. Disassembly revealed the connector seal had deteriorated, allowing water ingress that caused a micro-short between the terminals. Repair: Replaced the seat belt retractor assembly (pretensioner had shorted and failed), fitted a new waterproof connector with insulation treatment, and cleared the drainage holes beneath the seat. Fault cleared.
BYD DTC AI Analysis

Seat modification damaged the wiring harness

✓
One week after installing racing seats in their 2018 BYD Qin EV450, the owner saw DTC B1792-00. The technician found the pretensioner harness unsecured during the modification. The seat rail bracket had pinched the harness repeatedly, wearing through the insulation and shorting the core wire to ground. Repair: Cut out the damaged section, soldered the joint and insulated it with heat-shrink tubing. Re-secured the harness along the standard routing path with adequate clearance from moving parts. Cleared the code; operation normal.
BYD DTC AI Analysis

Pretensioner internal resistance drift due to ageing

✓
2017 Qin 100, 120,000 km. Intermittent DTC B1792-00: present when cold, clearing when hot. Pretensioner resistance dropped to 1.2Ω in cold conditions, returning to 2.5Ω when warm. Diagnosis: Moisture ingress and aging of the internal igniter propellant caused abnormal temperature coefficient. Fix: Replaced OEM driver's side seat belt retractor assembly. Fault eliminated. Note: Verify soft faults with multiple measurements across different temperature environments.
BYD DTC AI Analysis

Connector pin backed out causing short circuit

✓
Following accident repairs, the vehicle set DTC B1792-00. Inspection found the B-pillar pretensioner connector had been misaligned during reinstallation, causing one terminal to back out and bend, contacting the adjacent terminal and creating a short circuit. Repaired the pin, reinstalled it using a dedicated terminal removal tool, applied conductive paste to ensure good contact, and relocked the connector. Fault cleared.
Other Qin Plus 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.