AU
B164B-00

DTC B164B-00 indicates the airbag control unit (SRS ECU) detects an abnormally low-resistance path (typically <1Ω) from the front passenger seat belt pretensioner ignition circuit to body ground — Atto 8

Safety System

DTC B164B-00 indicates the airbag control unit (SRS ECU) detects an abnormally low-resistance path (typically <1Ω) from the front passenger seat belt pretensioner ignition circuit to body ground.

The pretensioner is a pyrotechnic safety device containing an igniter and a gas generator, with a normal resistance of approximately 2.0-3.0Ω.

A short to ground indicates damaged insulation on at least one of the two ignition circuit wires contacting vehicle body metal, or an internal short circuit within the pretensioner igniter.

The system classifies this fault as severe because: 1) the short circuit can cause unintentional pretensioner deployment, injuring the occupant; 2) it can prevent pretensioner deployment during a collision, causing a loss of restraint protection; 3) the SRS system enters fail-safe mode, which can disable the front airbags.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Damaged pretensioner wiring harness sleeve under the front passenger seat: Frequent fore-and-aft seat adjustment causes long-term bending of the wiring harness below the B-pillar or near the seat rail, wearing through the insulation and shorting it to the vehicle body metal.
  • 2Pretensioner connector water ingress and oxidation: Driving through water, a blocked sunroof drain tube, or deep interior cleaning allows liquid to seep into the front passenger pretensioner connector (usually located under the seat or behind the B-pillar trim), causing a short circuit between terminals or a short to ground.
  • 3Pretensioner internal igniter damaged: Physical impact, dropping, or aging caused a short circuit between the internal bridge wire and the housing, or moisture in the pyrotechnic charge abnormally reduced the resistance.
  • 4SRS control unit internal drive circuit fault: Airbag ECU internal pretensioner driver chip or power transistor breakdown causes a continuous low-level output signal.
  • 5Improper modification or repair: Retaining screws pierce the pretensioner wiring harness when installing seat heating, ventilation, or replacing seat covers; or an incompletely locked pretensioner connector after accident repairs allows terminals to back out and contact the metal bracket.
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the low-voltage battery negative terminal, wait at least 90 seconds (to fully discharge the SRS capacitor), and wear an anti-static wrist strap.
  • 2
    Visual inspection: Remove the front passenger seat (or lift the rear section only). Inspect the yellow pretensioner wiring harness connector under the seat and below the B-pillar (inside the door sill trim) for obvious damage, burn marks, or liquid ingress.
  • 3
    Connector isolation test: Disconnect the pretensioner connector. Use a digital multimeter to measure the resistance between the terminals on the pretensioner side (normal: 2.0-3.0 Ω). If the resistance is close to 0 Ω, replace the pretensioner assembly. Measure the resistance to ground on the wiring harness side (must be >1 MΩ). If continuity exists, inspect and repair the wiring harness.
  • 4
    Harness continuity check: Use a probe to measure the harness resistance between the SRS ECU connector (usually located in the lower center console or center tunnel) and the pretensioner connector (should be <1Ω). Measure the insulation resistance to ground for each of the two wires.
  • 5
    Substitute resistor verification: Connect a dedicated 2Ω substitute resistor (airbag simulator) to the pretensioner connector. Connect the battery, power on the vehicle, and read the fault code. If the code becomes a history code or disappears, the pretensioner is faulty.
  • 6
    SRS ECU inspection: If the wiring harness and pretensioner are normal, measure the voltage to ground and resistance at the corresponding SRS ECU pins. Replace the airbag control unit if necessary (requires programming and matching).
  • 7
    Repair and replacement: Repair the damaged wiring harness (wrap with two layers of high-temperature insulating tape and add corrugated conduit protection if necessary). Replace the damaged pretensioner (install a brand-new genuine part; do not reuse a triggered pretensioner).
  • 8
    System reset: Clear the fault code and perform the SRS system self-check cycle (turn the power to the ON position and verify the airbag warning lamp turns off after the self-check). Use the diagnostic tool to perform 'Crash Sensor Calibration' and 'Configuration Information Write' (if replacing the ECU or pretensioner).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat adjustment chafed the wiring harness, causing a short circuit.

✓
A 2017 BYD Qin EV300, 80,000 km. The owner reported the airbag warning light stayed on constantly. Scanned DTC B164B-00. Found that with the passenger seat adjusted fully rearward, the pretensioner wiring harness beneath the seat was rubbing against the metal edge of the seat rail. Long-term friction had worn through the yellow corrugated tubing, allowing the copper wires to short directly to the seat frame. Repositioned the harness, wrapped the damaged section with three layers of heat-resistant insulating tape, secured it with an additional plastic protective sleeve, and rerouted the wiring to avoid interference with moving parts. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Connectors on the water-damaged vehicle oxidised and short-circuited

✓
A 2018 Qin EV450. Poor front windscreen sealing allowed rainwater to leak into the passenger side A‑pillar interior trim and travel along the wiring harness into the pretensioner connector. Disassembly revealed severely oxidised (green) terminals inside the connector, causing a short circuit between the terminals and the connector metal housing. The warning light illuminated in wet weather and occasionally cleared when dry. Replaced the pretensioner wiring harness connector by cutting off the old plug, soldering on the new plug, and waterproofing the joint. Applied waterproof silicone grease to the pretensioner socket. Repaired the windscreen seal. The fault has not returned.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal damage to pretensioner after accident repair

✓
Replaced the front passenger seatbelt assembly (including pretensioner) on a 2017 BYD Qin 100 following front collision repairs, but the airbag warning light stayed on. Could not clear DTC B164B-00. Measured the new pretensioner resistance at 0.8Ω (abnormally low), indicating a parts quality defect or internal igniter short caused by impact during transport. Fitted a brand new genuine pretensioner, and resistance returned to normal at 2.3Ω. Cleared the DTC, and the system returned to normal. Caution: Pretensioners are explosive devices; avoid dropping during transport and storage.
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket seat heater installation pierced the wiring harness.

✓
The owner of a 2017 Qin 80 had a passenger seat heating pad installed at an auto parts market. The installer used self-tapping screws that were too long when securing the heating pad. The screws penetrated the seat foam and punctured the pretensioner wiring harness, causing a short to ground. The fault appeared the next day when the airbag light came on. Inspection found two unauthorised screws beneath the seat. One had pierced straight through the yellow pretensioner harness. Repair: removed the screws, replaced the entire pretensioner harness (replaced the whole harness for safety), rerouted the wiring away from the aftermarket parts, and cleared the fault codes.
BYD DTC AI AnalysisFrom Chinese market (translated)

SRS ECU internal drive circuit fault

✓
A 2017 Qin EV300 repeatedly logged DTC B164B-00, with the fault returning within days after each clear. Replaced the pretensioner and wiring harness without success. In-depth inspection revealed the passenger-side pretensioner driver chip inside the SRS ECU had shorted to ground, causing the ECU to continuously detect a false short-to-ground condition. Such faults typically result from previous voltage instability, such as reverse polarity or voltage surges during jump-starting. Replaced the airbag control unit and used a dedicated diagnostic scanner to write the VIN and configure the system. This completely resolved the fault.
Other Atto 8 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. Sources: [1]