AU
B1798-00

DTC B1798-00 indicates the front passenger seat belt second-stage pretensioner firing circuit resistance falls below the SRS control module threshold (typically under 1 — Qin Plus

Safety System

DTC B1798-00 indicates the front passenger seat belt second-stage pretensioner firing circuit resistance falls below the SRS control module threshold (typically under 1.0Ω or the manufacturer-calibrated value).

The second-stage pretensioner operates within a staged restraint system, deploying sequentially with the first stage during a severe collision to provide greater retraction force.

Low resistance indicates a circuit short to ground, an internal short in the pretensioner squib, a short between connector pins, or an abnormal ground path caused by damaged wire insulation.

Consequently, the SRS module detects a risk of unintended deployment (potential misfire or failure to reach design deployment energy).

The module then illuminates the airbag warning light and disables the front passenger airbag functions, severely compromising occupant restraint protection during a collision.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Front passenger seat belt pretensioner unit internal short circuit (moisture, aging, or manufacturing defects in the igniter cause internal resistance to drop abnormally to a near-short-circuit state)
  • 2Short to ground in the wiring harness under the seat or inside the B-pillar trim panel (frequent fore-and-aft movement of the front passenger seat crushes the harness insulation, or a metal bracket edge cuts the harness, causing the copper wire to contact vehicle body ground).
  • 3Pretensioner connector short circuit due to water ingress and corrosion (spilled drinks, car wash water ingress, or sunroof leaks creating a low-resistance path between the yellow SRS connector pins or a short to the housing)
  • 4SRS control module internal detection circuit fault (an A/D converter or sampling resistor fault incorrectly reads the pretensioner resistance as too low; actual measurement shows the pretensioner is normal).
  • 5Improper accident repair or unauthorized modification (e.g., piercing the pretensioner wiring harness during seat heating/ventilation installation, or using non-OEM parts with mismatched resistance after an accident)
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor. Wear an anti-static wrist strap. Do not measure the pretensioner directly using a multimeter resistance setting, as excessive trigger current may cause accidental deployment. Use a dedicated SRS diagnostic tool or ensure the multimeter current is below 1mA.
  • 2
    Fault status confirmation: Use VDS2000 or a dedicated BYD diagnostic tool to read freeze frame data. Confirm B1798-00 is a current fault (Active Code), not a historical fault. Record the displayed resistance value (e.g., 0.3Ω, 0.8Ω) to compare with the standard value (typically 2.0-3.0Ω).
  • 3
    Visual and connector inspection: Inspect the yellow SRS connector on the front passenger seat belt assembly (located under the seat or at the base of the B-pillar) for damage, broken locking tabs, water ingress, pin corrosion, backed-out pins, or bridging.
  • 4
    Pretensioner unit resistance measurement: Disconnect the pretensioner connector. Use a dedicated low-current ohmmeter to measure the resistance between the two pretensioner terminals. If the reading is below 1.0Ω (or the manufacturer's lower limit), this indicates an internal short circuit in the pretensioner. Replace the seat belt assembly (including the pretensioner).
  • 5
    Harness insulation check: Measure resistance between the pretensioner harness side (vehicle harness end) and body ground. Resistance must be infinite. If continuity exists, trace the circuit to the SRS module. Focus inspection on seat slide rail pinch points and bends inside the sill trim panel. Repair damaged insulation and rewrap the harness.
  • 6
    Swap verification test (if driver and front passenger configurations are identical): Swap the driver and front passenger pretensioners. If the fault code changes to B1797 (driver side), this confirms a faulty pretensioner unit. If the fault persists, check the SRS control module and wiring harness.
  • 7
    Repair and system verification: After replacing the faulty part, install the pretensioner using the special bolts and tighten to the specified torque (usually 7-10 N·m). Fully lock the connector (listen for a click). Reinstall the battery, clear the fault code, and perform the SRS system self-check cycle (turn the ignition switch ON, wait 6 seconds, and observe if the airbag warning light turns off). Finally, perform a road test to verify the repair.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 seat rails crush wiring harness, causing short circuit

✓
2018 Qin EV450 with 30,000 km. Airbag warning light on. Read DTC B1798-00, resistance 0.5Ω. Found the seat rail bracket edge pinching the second-stage pretensioner harness under the front passenger seat during fore-aft adjustment, damaging the insulation and causing a short to ground. Repair: Repaired the damaged harness (2 wires), insulated with double-layer heat shrink tubing, rerouted the harness with corrugated tubing protection, and secured it to the seat frame away from moving parts. Fault cleared.
BYD DTC AI Analysis

Sunroof leak caused pretensioner connector corrosion on Qin 100.

✓
2017 BYD Qin 100, southern region. B1798-00 set after rain. Sunroof drain hose aged and detached, letting water run down the A-pillar and pool in the passenger seatbelt pretensioner connector (inside sill trim). Connector pins oxidised with green copper corrosion, dropping resistance between pins to 0.8Ω. Repair: Cleaned pins with electronic cleaner and fine sandpaper, applied conductive anti-corrosion paste, replaced sunroof drain hose connector, sealed connector with waterproof tape. Fault resolved.
BYD DTC AI Analysis

Qin EV300 Second Stage Pretensioner Internal Igniter Short Circuit

✓
This Qin EV300 had no collision history when the SRS warning light came on during normal use. The diagnostic tool showed B1798-00. We measured the pretensioner resistance at only 0.6 Ω (standard: 2.3±0.3 Ω), indicating a short in the second-stage pretensioner's internal gas generator. Since the pretensioner and seat belt retractor are integrated, we replaced the front passenger seat belt assembly (part number: 69C-000000-XXX). We used new pretensioner mounting bolts (anti-loosening design) and tightened them to 9 N·m. After clearing the fault codes, the system returned to normal.
BYD DTC AI Analysis

Unsecured connector after accident repair caused intermittent fault

✓
After front-end collision repairs at a non-authorised shop, DTC B1798-00 appeared intermittently. Inspection found the second stage pretensioner connector was inserted but not fully locked during passenger airbag repair (locking tab not engaged). Road vibrations caused the connector to loosen, letting the pins touch the body metal and create low resistance. Fix: Reconnected the connector and confirmed the locking tab fully engaged. Secured it with cable ties to prevent loosening. Cleared the fault codes and tracked for one week with no recurrence.
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.