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 U

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 U indicates low resistance in the front passenger seat belt second-stage pretensioner firing circuit. This is a medium-severity SRS fault that can 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 trim. 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 — Seal U
  • 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 body ground).
  • 3Pretensioner connector short circuit due to water ingress and corrosion (spilled drinks, car wash water ingress, or sunroof leaks causing 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 a false low pretensioner resistance reading; 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 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 with a multimeter resistance setting, as excessive trigger current can 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 BYD dedicated 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 against 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) for damage, broken locking tabs, signs of water ingress, pin corrosion, pin back-out, 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. 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 side (vehicle harness end) and body ground. 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 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 to the specified torque (typically 7-10 N·m). Ensure the connector locks fully (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 verify 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 Seal U Fault Codes
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.