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B164F-00

B164F-00 indicates the measured resistance of the front passenger seat belt pretensioner is 0 ohms, signifying a short circuit fault in the pretensioner circuit (short to ground or internal short) — Seal U

Safety System

B164F-00 indicates the measured resistance of the front passenger seat belt pretensioner is 0 ohms, signifying a short circuit fault in the pretensioner circuit (short to ground or internal short).

In the SRS (airbag) system, normal pretensioner resistance is typically 2.0-3.0 ohms.

The ECU monitors circuit current to determine component status.

A 0-ohm resistance indicates an abnormal current path.

The ECU registers a short circuit fault, illuminates the airbag warning light, and may disable the passenger airbag and pretensioner functions, severely compromising occupant protection during a collision.

Differentiate this fault from "resistance too high" (open circuit).

A 0-ohm reading typically indicates a hard short circuit or a direct harness short to ground.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Pretensioner internal short circuit: The front passenger seat belt pretensioner squib shorts internally, causing resistance to approach 0. Component aging or manufacturing defects usually cause this.
  • 2Harness chafed to ground: Frequent fore-and-aft seat adjustment wears through the insulation on the front passenger seat pretensioner harness (yellow dedicated harness), causing direct contact with the body metal and a short to ground.
  • 3Connector short circuit due to water ingress: Vehicle wading or improper cleaning causes water to enter the pretensioner connector under the seat (usually located near the seat slide rail), resulting in a short circuit between pins or a short to ground.
  • 4SRS ECU internal monitoring circuit fault: A faulty internal monitoring chip or sampling resistor in the airbag control unit causes a false short-circuit report, while actual pretensioner resistance is normal.
  • 5Incorrect operation: When directly measuring the pretensioner with a multimeter set to ohms, failing to follow specifications or measuring a damaged pretensioner may result in a 0 Ω reading. (Note: Never use a standard multimeter for measurement; use dedicated diagnostic equipment.)
What To Do
  • 1
    Safe power down: Turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds (to fully discharge the SRS capacitor). Never work on the airbag system while energized.
  • 2
    Visual inspection: Remove the front passenger seat (or lift the seat carpet) and inspect the yellow SRS wiring harness under the seat for obvious wear, cuts, or crush marks. Focus on the seat slide rail mounting points and harness bend points.
  • 3
    Connector inspection: Disconnect the pretensioner connector (special connector with shorting bar). Inspect inside the connector for water ingress, corrosion, metallic debris, or bent pins causing a short circuit. Clean or replace the connector if necessary.
  • 4
    Resistance measurement: Use a dedicated SRS diagnostic tool or a high-precision low-current ohmmeter (range <250mA) to measure the pretensioner unit resistance. If it reads 0 ohms, replace the front passenger seat belt assembly (including the pretensioner). If it reads 2-3 ohms (normal), check the wiring harness.
  • 5
    Harness continuity test: Measure the resistance to ground of the pretensioner harness terminal. Resistance must be infinite. If continuity exists (0 ohms), trace the wiring to locate the damaged point, then repair or replace the harness. Also measure continuity between both ends of the harness to rule out an open circuit.
  • 6
    ECU verification: If the wiring harness and pretensioner are normal, connect a spare SRS ECU to determine if the control unit is reporting a false fault. If testing confirms an ECU fault, replace the airbag control module and perform coding configuration.
  • 7
    System reset: After repair, reconnect all components and the battery. Clear the fault code using the diagnostic tool. Perform the SRS system self-check (normally, after turning the ignition switch to ON, the warning lamp illuminates for 6 seconds and then turns off). Perform a simulated crash test to verify.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV300 seat wiring harness chafed and shorted

✓
The airbag warning light on the dashboard stayed on. Read fault code B164F-00. Found the yellow SRS wiring harness beneath the passenger seat had worn through its insulation at the seat track retaining clip, exposing the copper core and shorting the pretensioner circuit to ground. Repaired the damaged harness using heat shrink tubing and rerouted the wiring to avoid rubbing against metal edges. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin 80: Replaced pretensioner due to internal short circuit

✓
Customer reported the airbag warning light was on. Scan revealed DTC B164F-00. Disconnected the pretensioner connector and measured 0.2 ohms resistance across the pretensioner pins (normal 2.3 ohms). Diagnosed a short circuit in the pretensioner's internal pyrotechnic element. Replaced the front passenger seat belt assembly (including pretensioner). The new part measured 2.4 ohms. Installed the assembly and cleared the fault code. The system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Connector corrosion due to water wading

✓
After driving through water, the airbag warning light came on with DTC B164F-00. Inspection found water and corrosion inside the pre-tensioner connector under the front passenger seat, causing the pins to short together. Cleaning and blow-drying the connector did not stabilise the resistance readings. Replaced the pre-tensioner wiring harness connector (with shorting link) and waterproofed the related wiring to resolve the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Troubleshooting SRS ECU False Fault Reports

✓
DTC B164F-00 kept recurring. Replaced the pretensioner and wiring harness but the fault persisted. Measured the monitoring signal from the SRS ECU to the pretensioner with an oscilloscope; the waveform was abnormal. Replaced the airbag control module (requires VIN reconfiguration and coding). The fault code did not recur, confirming the false trigger was caused by an internal monitoring circuit fault in the ECU.
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. Sources: [1]