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 — Atto 8

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 Atto 8 indicates low resistance in the front passenger seat belt second-stage pretensioner firing circuit. This is a medium-severity SRS fault that may disable passenger airbag functions and reduce crash protection. Common causes include an internal short in the pretensioner or damaged wiring under the seat or B-pillar. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Front passenger seat belt pretensioner unit internal short circuit (igniter moisture, aging, or manufacturing defects causing 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 front passenger seat movement damages the harness insulation, or a metal bracket edge cuts the harness, causing copper wire to contact body ground).
  • 3Pretensioner connector short circuit due to water ingress and corrosion (spilled drinks, car wash water, or sunroof leaks create a low-resistance path between the yellow SRS connector pins or a short to the housing).
  • 4SRS control module internal detection circuit fault (A/D converter or sampling resistor malfunction 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 retrofitting seat heating/ventilation, or using non-genuine parts with mismatched resistance after an accident)
What To Do
  • 1
    Safety Preparation: Disconnect the battery negative terminal and wait at least 90 seconds for the SRS capacitor to fully discharge. Wear an anti-static wrist strap. Do not measure the pretensioner directly with a multimeter set to resistance, as excessive trigger current can cause accidental deployment. Use a dedicated SRS diagnostic tool or ensure the multimeter current is below 1 mA.
  • 2
    Fault status confirmation: Use VDS2000 or a dedicated BYD diagnostic tool to read the freeze frame data. Confirm B1798-00 is a current fault (Active Code) and not a historical 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 on the front passenger seat belt assembly (located under the seat or at the base of the B-pillar). Verify the connector is intact and check for a broken locking tab, signs of water ingress, terminal corrosion, terminal back-out, or bridging.
  • 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), the pretensioner has an internal short circuit. Replace the seat belt assembly (including the pretensioner).
  • 5
    Harness insulation check: Measure the resistance between the pretensioner harness side (vehicle harness end) and body ground. The resistance must be infinite. If continuity exists, trace the circuit to the SRS module, focusing on 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 remains, 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 (typically 7-10 N·m). Ensure the connector fully locks (listen for a click). Reinstall the battery, clear the fault codes, 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 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 Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.