AU
B1799

DTC B1799 indicates the squib circuit resistance of the front passenger-side second-stage seat belt pretensioner (usually located under the front passenger seat or lower B-pillar) exceeds the SRS ECU threshold (standard value: 2 — Atto 3

Safety System

DTC B1799 indicates the squib circuit resistance of the front passenger-side second-stage seat belt pretensioner (usually located under the front passenger seat or lower B-pillar) exceeds the SRS ECU threshold (standard value: 2.0 Ω ± 0.4 Ω; typically triggers at >2.4 Ω).

This passive safety fault in the Supplemental Restraint System (SRS) means the ECU detects a high-resistance condition in the pretensioner circuit.

Poor contact, a partial open circuit in the wiring, or an aging internal pretensioner squib can cause this condition.

This fault may prevent the second-stage pretensioner from deploying correctly during a collision, reducing occupant restraint protection.

The SRS warning light remains illuminated to alert the driver.

The B1799 fault code on the Atto 3 indicates high resistance in the front passenger-side second-stage seat belt pretensioner circuit, part of the SRS safety system. Severity is medium, as the pretensioner may not deploy correctly in a crash. Common causes include a loose or oxidized pretensioner connector, or damaged wiring near the seat or B-pillar. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Pretensioner connector loose or terminal oxidized: The pretensioner plug under the front passenger seat or in the B-pillar area loosens due to vibration, or terminal surface oxidation or water ingress increases contact resistance (contact resistance exceeding 0.5Ω causes total resistance to exceed the limit).
  • 2Partial open circuit or poor contact in the wiring harness: Prolonged bending or compression of the pretensioner wiring harness inside the B-pillar trim panel or near the seat slide rail breaks the internal copper strands. This reduces the effective conductive cross-section and creates a high-resistance point.
  • 3Pretensioner internal squib aging: Age or environmental factors oxidize the internal resistance wire of the pretensioner squib, causing the resistance value to drift above the upper limit.
  • 4Poor ground circuit: The pretensioner circuit grounds through the vehicle body. Loose or corroded ground points, such as G301/G302, increase total circuit resistance.
  • 5Previous repair issues: failing to fully lock the pretensioner connector during seat or B-pillar trim removal and installation, or pinching the wiring harness in a sheet metal gap, causing hidden damage.
What To Do
  • 1
    Safety preparation: Switch off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental deployment.
  • 2
    Fault confirmation: Connect the BYD VDS diagnostic tool. Enter the SRS system to read fault codes. Confirm B1799-00 and freeze frame data (record the specific resistance value). Check for accompanying fault codes.
  • 3
    Locate the component: Remove the front passenger seat or lower B-pillar trim panel. Locate the second-stage seat belt pretensioner (usually marked 'Pretensioner-2nd Stage').
  • 4
    Visual inspection: Check the pretensioner connector for looseness, the locking tab for breakage, the wiring harness for signs of crushing or abrasion, and the terminals for green oxidation or signs of water ingress.
  • 5
    Resistance measurement: Disconnect the pretensioner connector. Use a precision multimeter (0.1Ω accuracy) to measure the resistance between the two terminals of the pretensioner body. Standard value: 2.0Ω±0.4Ω (at 20℃ ambient). If >2.4Ω, the pretensioner body is faulty; if normal, check the wiring.
  • 6
    Circuit test: Measure wiring harness continuity between the pretensioner connector and the SRS ECU. Verify the harness continuity resistance at the B-pillar hinge is <0.5Ω. Check for high-resistance points or intermittent open circuits.
  • 7
    Ground check: Check pretensioner circuit ground points G301/G302. Clean the ground surfaces and tighten the bolts (typical standard torque: 8-10 N·m). Ensure ground resistance is <0.1 Ω.
  • 8
    Repair/replace: If the connector is oxidized, clean it with electrical contact cleaner and apply conductive grease; if the wiring harness is damaged, repair or replace it; if the pretensioner unit resistance exceeds the limit, replace it with an OEM pretensioner assembly (Note: The pretensioner is an explosive component. Handle the old part according to dangerous goods transport regulations).
  • 9
    Verification test: Reconnect all connectors and the 12V battery. Turn the ignition switch ON. Use VDS to clear the fault code. Perform the 'SRS system self-check'. Confirm B1799 does not return and the instrument cluster airbag warning light turns off. Perform a road test to confirm no intermittent faults exist.
Real-World Cases
BYD DTC AI Analysis

BYD Qin Pro B1799 DTC – Oxidized Connector Causing High Resistance

✓
A 2019 BYD Qin Pro arrived with the airbag warning light constantly on. VDS retrieved DTC B1799-00. The technician removed and inspected the pretensioner connector beneath the front passenger seat and found visible green oxide inside—the vehicle had previous water exposure. The pretensioner measured 2.1 Ω (normal), but the harness side showed 1.2 Ω contact resistance. The technician cleaned the connector terminals with WD-40 electronic cleaner, applied conductive grease, and re-locked the connector. After clearing the DTC, the system self-test passed and the fault cleared.
Original source ↗
BYD DTC AI Analysis

BYD Song MAX B1799 Fault - B-Pillar Wiring Harness Crush Damage

✓
A 2020 Song MAX had an intermittently illuminated airbag warning light. The diagnostic scan showed code B1799-00 (historical). Inspection found signs the passenger side B-pillar lower trim had been removed (the owner had taken it off earlier for window tinting). Disassembling the B-pillar revealed the pre-tensioner harness trapped between the trim clip and sheet metal, damaging the insulation and partially fracturing the internal copper wires—about three strands remained connected. Resistance across this section measured 3.8Ω (normal is <0.5Ω). Repaired the wiring by cutting out the damaged section, soldering in an extension, and insulating with double-layer heat shrink tubing. Rerouted the harness to prevent pinching. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM B1799 – High Circuit Resistance from Poor Ground

✓
A 2021 Tang DM showed an airbag warning after accident repairs; VDS reported B1799-00. The vehicle had prior sheet metal work on the passenger-side A-pillar. The pretensioner connector checked normal and the unit measured 2.0Ω, but the negative circuit-to-body resistance was 2.5Ω (should be <0.1Ω). Traced to ground G302 under the passenger seat—the body shop never cleaned it during repairs, so paint residue caused poor contact. Fix: Sanded the ground point to bare metal and retorqued the bolt to 9N·m. Resistance dropped to 0.05Ω. Cleared the DTC; fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Yuan EV B1799 — Seatbelt pre-tensioner resistance drift due to aging

✓
A 2019 Yuan EV with 60,000 km had the airbag warning light on constantly, storing DTC B1799-00. Resistance at the pretensioner connector measured 3.2Ω (significantly high). Disconnecting the plug and measuring directly across the pretensioner body showed 3.1Ω (specification 2.0±0.4Ω), confirming internal igniter aging caused resistance drift. Wiring harness and connectors were normal. Replaced the front passenger second-stage seatbelt pretensioner assembly (Part No.: 5A-5826000-XX). The new part measured 1.9Ω. After installation, cleared the fault codes and the SRS self-test passed.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro B1799 Intermittent Fault – Resistance Fluctuation Due to Loose Connection

✓
A 2020 Song Pro had an intermittent airbag warning light. VDS read historical fault code B1799-00 (current resistance 2.6Ω, borderline high). The pretensioner connector under the front passenger seat had a broken locking tab; the plug was not fully seated, causing an intermittent connection. Resistance fluctuated between 1.8Ω and 4.5Ω when moving the harness. Replaced the pretensioner connector (with wiring harness pigtail) and ensured full lock. Cleared the fault codes and road-tested continuously for 3 days; the fault did not recur.
Original source ↗
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.