AU
B1797

DTC B1797 indicates the SRS (airbag) control module detects a 0-ohm circuit resistance in the front passenger second-stage seat belt pretensioner (typically the igniter/squib) — Seal U

Safety System

DTC B1797 indicates the SRS (airbag) control module detects a 0-ohm circuit resistance in the front passenger second-stage seat belt pretensioner (typically the igniter/squib).

Normal seat belt pretensioner resistance is 1.5-3.0 ohms.

A 0-ohm resistance indicates a short circuit (short to ground or internal short) within the pretensioner or its wiring.

This fault forces the SRS into degraded protection mode.

The front passenger airbag may fail to deploy, severely compromising crash safety.

The second-stage pretensioner works with the airbag to rapidly retract the seat belt during a collision, limiting forward occupant movement.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Pretensioner igniter internal short circuit: Moisture or aging of the pyrotechnic charge inside the seat belt pretensioner causes a short circuit between the terminals, reducing resistance to 0 ohms.
  • 2Wiring harness damaged and shorted to ground: Frequent door opening and closing wears the insulation on the seat belt pretensioner wiring harness near the B-pillar, shorting it to the vehicle body metal.
  • 3Connector water ingress and corrosion: Water enters the pretensioner connector during car washes or when water floods the front passenger-side floor, causing a short circuit between pins.
  • 4Improper repair procedure: Directly measuring the pretensioner circuit with a multimeter resistance setting during previous airbag system repairs (use a dedicated diagnostic tool), damaging the pretensioner.
  • 5SRS module monitoring fault: Airbag control module internal monitoring circuit fault, falsely reporting a pretensioner short circuit (confirm via swap test).
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the battery negative terminal, and wait at least 90 seconds to completely discharge the SRS capacitor and prevent accidental deployment.
  • 2
    Inspection location: Remove the front passenger-side B-pillar trim and locate the second-stage seat belt pretensioner connector (usually a yellow connector located below the seat belt retractor or in the middle of the B-pillar).
  • 3
    Visual inspection: Check the pretensioner wiring harness for damage or crush marks, and check the connector for water ingress, corrosion, or bent pins.
  • 4
    Resistance measurement: Disconnect the pretensioner connector and use a digital multimeter to measure the resistance directly across the two pretensioner terminals (normal: 1.5-3.0 Ω; 0 Ω indicates an internal short circuit, replace the pretensioner).
  • 5
    Harness continuity test: Measure the resistance to ground and supply voltage at the harness-side connector to check for a short circuit or short to ground in the harness.
  • 6
    Component replacement: If diagnostics confirm an internal short circuit in the pretensioner, replace the front passenger-side seat belt assembly (do not replace the pretensioner separately). If the wiring harness is faulty, repair or replace the wiring harness.
  • 7
    System verification: Reconnect all connectors, restore power, use VDS or a dedicated diagnostic tool to clear the fault code, perform an SRS system self-check, and verify with a road test.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM B1797 Fault Code After Water Fording

✓
2021 BYD Tang DM drove through approximately 40 cm of floodwater during a heavy rainstorm, triggering the airbag warning light. Scanner read DTC B1797 (passenger side second stage pretensioner resistance 0). Found water in the SRS harness connector beneath the passenger seat; oxidized pins caused a short. Cleaned the connector, dried it with compressed air, sprayed electronic cleaner, applied conductive grease, and reconnected. Fault cleared. Check the door seals and floor drain holes.
BYD DTC AI Analysis

BYD Song MAX pretensioner short circuit after accident repair

✓
A 2019 Song MAX was in a collision that deployed the passenger side airbag. After an external shop replaced the seatbelt assembly, the warning light came on. Scanned DTC B1797. Inspection found the new passenger seatbelt pretensioner connector not fully seated, and the non-genuine part had abnormal internal resistance (measured 0.2Ω). Replaced with a genuine passenger seatbelt assembly; resistance measured 2.1Ω (normal). Cleared the DTC and the system returned to normal.
BYD DTC AI Analysis

Worn wiring harness causes intermittent short circuit in BYD Yuan EV

✓
2019 BYD Yuan EV intermittent airbag warning light, sometimes after driving over speed bumps. Scan tool retrieved historical fault code B1797. Inspection of the passenger side B-pillar wiring found the seatbelt pretensioner harness rubbing against the B-pillar metal frame, damaging the insulation and causing an intermittent short to ground. Repair: Wrapped the damaged section with insulation tape, rerouted the harness and added a protective sleeve, then secured it to prevent contact with the body. Fault eliminated.
BYD DTC AI Analysis

Seat modification triggers pretensioner fault in Qin Pro

✓
2020 Qin Pro owner installed a DIY front passenger seat heater. While routing the wiring, the heater power wire pierced the SRS harness, shorting the pretensioner circuit to chassis and triggering DTC B1797. Inspection found obvious puncture damage in the under-seat harness with damaged insulation on the pretensioner lines. Repaired the SRS harness using soldered joints and heat-shrink tubing, separated the heater wiring from the SRS harness, and cleared the fault. Never mix SRS wiring with non-safety system circuits.
Other Seal U 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.