AU
B1799-00

DTC B1799-00 indicates the SRS (Supplemental Restraint System) ECU detects the front passenger-side second-stage seat belt pretensioner circuit resistance exceeds the normal upper limit (typically >3 — Atto 8

Safety System

DTC B1799-00 indicates the SRS (Supplemental Restraint System) ECU detects the front passenger-side second-stage seat belt pretensioner circuit resistance exceeds the normal upper limit (typically >3.0-3.5Ω, normal range is 2.0-3.0Ω).

The second-stage pretensioner is a critical component of the airbag system.

During a severe collision, a pyrotechnic charge generates a rapid tightening force, working with the first-stage pretensioner to provide enhanced occupant restraint.

Excessive resistance typically indicates a high-resistance circuit contact, a partial open circuit, or an aging internal resistance wire within the pretensioner.

This causes the ECU to identify a pretensioner failure risk, illuminate the airbag warning light, and potentially disable the front passenger-side airbag and pretensioner functions.

During a collision, the second-stage pretensioner may fail to deploy properly, allowing excessive forward occupant movement and increasing injury risk.

The B1799-00 fault code on the Atto 8 indicates the SRS ECU has detected excessive resistance in the front passenger-side second-stage seat belt pretensioner circuit. Severity is medium because the airbag warning light may come on and the passenger pretensioner or airbag may not work correctly in a crash. Common causes include an aging pretensioner resistance element or damaged under-seat wiring. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Aging internal resistance element in the seat belt pretensioner or near open circuit: Long-term use or moisture ingress causes the pretensioner squib resistance wire value to drift and exceed the ECU monitoring threshold.
  • 2Mechanical damage to under-seat wiring harness: During front passenger seat fore/aft adjustment, the seat bottom rubs against and pinches the frame-mounted pretensioner wiring harness, causing partial breakage of the internal copper wires or poor contact.
  • 3Poor connection: The pretensioner connector under the B-pillar or seat has oxidized pins, looseness, corrosion from water ingress, or a failed locking tab, causing increased contact resistance.
  • 4Non-genuine part resistance specification mismatch: The resistance value of an aftermarket seat belt assembly pretensioner installed after accident repairs does not match the factory calibration, or the repair used a wiring harness repair part with a different resistance value.
  • 5Wiring harness excessively bent or improperly secured: Vehicle modifications (such as installing floor coverings or seat covers) pinched the pretensioner wiring harness, or improper harness routing during accident repairs increased local resistance.
What To Do
  • 1
    Connect the VDS2000 or VDS6000 diagnostic tool to the vehicle and read the DTC B1799-00 status. Confirm whether it is a current or history fault, and record the resistance value in the freeze frame data (typically 3.5-5.0 Ω).
  • 2
    Disconnect the battery negative terminal and wait at least 90 seconds for the SRS backup power supply to fully discharge. This ensures safe operation and prevents accidental airbag deployment.
  • 3
    Locate the front passenger second-stage seat belt pretensioner (on Qin series models, usually located inside the lower B-pillar trim panel or at the seat frame connection). Visually inspect the connector for looseness, oxidized or discolored pins, and internal water marks or corrosion.
  • 4
    Use a multimeter to measure the resistance across the pretensioner terminals. The standard value is 2.0±0.1Ω to 3.0±0.1Ω (refer to the vehicle repair manual for exact specifications). If the measured value is >3.5Ω, proceed to the next diagnostic step.
  • 5
    Disconnect the pretensioner connector and directly measure the pretensioner resistance. If the resistance is normal (2.0-3.0Ω), check the wiring harness: inspect for crushing or damage, focusing on the seat slide rail mounting bolts and under the carpet. Measure harness continuity and resistance using a multimeter (must be <1Ω).
  • 6
    If the wiring harness is damaged, use a genuine wiring harness repair kit to replace the connector or repair the damaged wire. Ensure solder joint resistance is <0.5Ω, and apply waterproof tape and corrugated conduit to reinforce protection. If the pretensioner unit resistance is too high, replace the front passenger seat belt assembly (including the second-stage pretensioner) with a genuine part. Do not use aftermarket parts.
  • 7
    Reconnect all connectors, fully engage the locks (listen for a 'click'), and restore the battery connection.
  • 8
    Use the diagnostic tool to clear the fault code, perform the SRS system self-check procedure, and verify B1799-00 does not recur. Read the data stream to confirm the pretensioner resistance value is within the normal range.
  • 9
    Perform a road test simulating bumpy roads and seat adjustments. Confirm the airbag warning light remains off and the system operates normally.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM pretensioner internal resistance aging caused high resistance.

✓
At 80,000 km, the airbag warning light stayed on constantly. VDS read DTC B1799-00. The technician measured front passenger second-stage pretensioner resistance at 3.5Ω, outside the standard 2.0-3.0Ω range. The B-pillar lower harness connector showed no oxidation or looseness, and seat wiring had no damage. Diagnosed the fault as pretensioner internal resistance wire aging causing resistance drift. Replaced the OEM front passenger seatbelt assembly. Post-repair resistance measured 2.2Ω. Cleared the fault codes; system self-check passed and the warning light went out.
Original source ↗
BYD DTC AI Analysis

Song MAX seat track pinches wiring harness, causing intermittent high resistance

✓
Airbag warning light illuminates intermittently, typically on cold starts and clearing after driving some distance. VDS logged B1799-00 as an intermittent fault. The technician performed a harness wiggle test; wiggling the wiring beneath the passenger seat reproduced the fault. Disassembly revealed the seat rail mounting bolt crushing the seatbelt pretensioner harness, partially fracturing the internal copper wires. Contact resistance fluctuated between 2.5-4.5Ω with seat position changes. Repaired the damaged harness, rerouted the wiring clear of the seat rail travel range, and protected it with waterproof tape and corrugated tubing. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Resistance mismatch in aftermarket parts after Qin EV accident repair

✓
After front collision repairs, the airbag warning light stayed on. VDS read B1799-00 (resistance too high) and B1798-00 (resistance too low). The passenger seatbelt assembly was an aftermarket part; the pretensioner measured 3.8Ω and the connector was loose. Replaced it with a genuine OEM unit, seated the connector fully and locked it, and measured 2.1Ω. Cleared the codes and the SRS self-test passed. Use genuine OEM SRS parts for accident repairs.
BYD DTC AI Analysis

Loose connector lock tab on Tang DM caused contact resistance fluctuation

✓
Airbag warning light intermittently illuminated on rough roads; normal on flat surfaces. VDS read B1799-00 as a history fault. Inspection found the passenger-side second-stage pretensioner connector lock loose—vehicle vibration caused slight plug displacement and poor contact. Oscilloscope monitoring caught resistance spiking to 4.2Ω during the fault. Replaced the pretensioner connector using a genuine wiring harness repair kit, secured the connection, and applied conductive grease to the pins to prevent oxidation. Road testing on rough surfaces after repair confirmed the fault cleared.
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.