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 — Seal 6 EV

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.

The B1798-00 fault code on the Seal 6 EV indicates low resistance in the front passenger seat belt second-stage pretensioner firing circuit. This is a medium-severity SRS fault because it can disable passenger airbag functions and reduce crash protection. Common causes include an internal short in the pretensioner or damaged wiring shorting to ground under the seat or B-pillar. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Front passenger seat belt pretensioner unit internal short circuit (igniter moisture, aging, or manufacturing defects cause internal resistance to drop abnormally to a near-short-circuit state)
  • 2Short circuit 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 pinches and damages the harness insulation, or a metal bracket edge cuts the harness, causing copper wire to contact the 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 causes the module to incorrectly read 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 when installing seat heating/ventilation, or using non-genuine parts with mismatched resistance after an accident)
What To Do
  • 1
    Safety Preparation: Disconnect the negative battery 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 in resistance mode, as excessive 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 the dedicated BYD diagnostic tool to read the freeze frame data. Confirm B1798-00 is a current fault (Active Code) rather than a history fault. Record the displayed resistance value (e.g., 0.3Ω, 0.8Ω) to compare with the standard value (usually 2.0-3.0Ω).
  • 3
    Visual and connector inspection: Inspect the yellow SRS connector of the front passenger seat belt assembly (located under the seat or at the bottom of the B-pillar). Verify the connector is intact and check for broken locking tabs, water ingress, and corroded, recessed, or bridged pins.
  • 4
    Pretensioner unit resistance measurement: Disconnect the pretensioner connector and use a dedicated low-current ohmmeter to measure the resistance between the two pretensioner terminals. If the reading is below 1.0 Ω (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 the resistance between the pretensioner harness (vehicle harness side) and body ground. The resistance must be infinite. If continuity exists, trace the circuit to the SRS module. Inspect pinch points at the seat slide rail and bends inside the sill trim panel. Repair damaged insulation and rewrap the harness.
  • 6
    Swap verification test (if driver and passenger configurations are identical): Swap the driver and passenger pretensioners. If the fault code transfers to B1797 (driver side), the pretensioner unit is faulty. If the fault persists, check the SRS control module and wiring harness.
  • 7
    Repair and system verification: After replacing the faulty component, 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). Reconnect the battery, clear the fault code, and perform an 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 for verification.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 seat rails crush wiring harness, causing short circuit

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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.

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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

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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

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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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV overview →
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.