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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
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

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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 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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.