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 3

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 3 indicates low resistance in the front passenger seat belt second-stage pretensioner circuit. Severity is medium because the airbag warning light may come on and front passenger restraint protection can be reduced. Common causes include an internal short in the pretensioner or damaged under-seat/B-pillar wiring shorting to ground. The recommended fix is to visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Front passenger seat belt pretensioner assembly internal short circuit (igniter moisture, aging, or manufacturing defects 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 pinches and damages the harness insulation, or a metal bracket edge cuts the harness, causing the copper wire to contact body ground).
  • 3Pretensioner connector short circuit caused by water ingress and corrosion (spilled drinks, water ingress during car washing, or a sunroof leak creates 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 fault causes false detection of low pretensioner resistance; actual measurement confirms the pretensioner is normal)
  • 5Improper collision repair or unauthorized modification (e.g., puncturing the pretensioner wiring harness when installing seat heating/ventilation, or using non-genuine parts with mismatched resistance after a collision)
What To Do
  • 1
    Safety preparation: Disconnect the 12V 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 can cause accidental deployment. Use a dedicated SRS diagnostic tool or verify the multimeter current is below 1 mA.
  • 2
    Fault Status Confirmation: Use VDS2000 or a BYD dedicated 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 against 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). Verify the connector is intact and check for a broken locking tab, water ingress, pin corrosion, pin recession, or bridging.
  • 4
    Pretensioner unit resistance measurement: Disconnect the pretensioner connector. Measure the resistance between the two pretensioner terminals using a dedicated low-current ohmmeter. A reading below 1.0 Ω (or the manufacturer's lower limit) 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 side (vehicle harness end) and body ground. The resistance must be infinite. If continuity exists, trace the circuit to the SRS module. Inspect the 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 remains, check the SRS control module and wiring harness.
  • 7
    Repair and system verification: After replacing the faulty part, install the pretensioner using dedicated bolts to the specified torque (usually 7-10 N·m). Ensure the connector locks fully (listen for a click). Reconnect 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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.