AU
B17601B

DTC B17601B indicates the airbag control unit (SRS ECU) detects a disconnected left front curtain airbag (located inside the driver-side roof rail), a communication interruption, or an abnormal resistance value — Seal U

Safety System

DTC B17601B indicates the airbag control unit (SRS ECU) detects a disconnected left front curtain airbag (located inside the driver-side roof rail), a communication interruption, or an abnormal resistance value.

This is an airbag system hard fault, meaning the left curtain airbag may fail to deploy during a side impact, resulting in a loss of occupant head protection.

The SRS ECU typically triggers this fault upon detecting infinite airbag inflator circuit resistance (open circuit) or resistance exceeding the normal threshold (standard value approximately 2.0-3.0 Ω) for longer than the specified time.

Possible causes include physical wiring disconnections, module damage, or incorrect configuration.

Inspect and repair immediately.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left front side curtain airbag module connector loose or making poor contact (located above the left A-pillar or front of the headliner; common after water ingress or interior trim removal and installation)
  • 2Airbag squib internal open circuit or abnormal resistance (broken clock spring inside the module causing resistance >10Ω or infinite resistance)
  • 3Open circuit in the roof wiring harness or A-pillar wiring harness (copper core breaks at the A-pillar routing hole due to frequent bending and wear, or a detached retaining clip pulls the harness)
  • 4Short to ground, short to power, or high resistance in the communication line between the SRS control unit and the airbag module (LIN or dedicated communication line fault)
  • 5Vehicle configuration code error (ECU software coding does not match the installed side curtain airbag configuration; commonly occurs when failing to perform coding configuration after replacing the ECU or airbag module)
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the negative battery terminal, wait at least 90 seconds (to ensure the SRS capacitor fully discharges), and wear an anti-static wrist strap.
  • 2
    Initial diagnosis: Connect the BYD dedicated diagnostic tool (VDS or ED400). Read the B17601B freeze frame data (record vehicle speed, temperature, and voltage at the time of the fault). Confirm whether the fault is a hard fault (Present) or an intermittent fault (History).
  • 3
    Visual inspection: Check the instrument panel SRS warning light status. Remove the left A-pillar trim and the front edge of the headliner. Verify the left front side curtain airbag module white/yellow connector is fully locked. Inspect the terminals for oxidation, backed-out pins, or water ingress corrosion.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector (located under the centre console or behind the centre armrest box). Use a digital multimeter to measure the resistance between the left front side curtain airbag circuit pins (typically a specific pair of coloured wires). Normal resistance is 2.0-3.0Ω. An infinity (OL) reading indicates an open circuit in the wiring or module.
  • 5
    Circuit continuity test: Measure wiring harness continuity between the airbag module and ECU connectors. Inspect wiring harness integrity, focusing on the A-pillar hinge and headliner harness fixing points. Measure harness insulation resistance to ground and power. Resistance must be >10MΩ.
  • 6
    Component replacement verification: If the wiring harness is normal, install a known-good side curtain airbag module for testing (or measure the original module resistance to confirm an open circuit). After replacement, perform "System Configuration" and "Coding Write".
  • 7
    System Reset and Verification: Restore all connections and turn on the power. Clear the fault code using the diagnostic tool. Perform the 'SRS system self-test' and 'crash sensor calibration'. Verify DTC B17601B does not return and the SRS warning light turns off.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV: Loose left front side curtain airbag connector caused DTC B17601B

✓
A 2019 Qin EV came in with the SRS warning light constantly on. Read DTC B17601B. The owner reported the headliner had recently been removed and reinstalled at a repair shop due to a sunroof leak. The technician removed the left A-pillar trim and found the white 2-pin connector for the left front side curtain airbag module was not fully locked, with slight terminal oxidation. Cleaned the terminals and reconnected securely (audible click), cleared the codes, and the SRS light went out. The fault did not recur during multiple road tests. Diagnosis: Intermittent open circuit caused by improper connector installation during interior trim work.
BYD DTC AI Analysis

BYD E2 roof wiring harness chafed through, causing open circuit and intermittent fault

✓
2020 model E3 (same platform as E2). SRS warning light intermittent. Diagnostic tool showed B17601B as history fault. Fault reproduced easily on rough roads. Removed headliner; found left front side curtain airbag wiring harness at B-pillar mounting clip had insulation worn from long-term vibration, copper core partially fractured presenting ~15Ω high impedance. Replaced headliner wiring harness assembly and re-secured routing to avoid sharp metal edges. Fault completely eliminated.
BYD DTC AI Analysis

BYD E3: Configuration error after airbag module replacement caused false alarm

✓
An E3 had its left front side curtain airbag and SRS ECU replaced following an accident. B17601B persisted after clearing fault codes. The new airbag module part number matched the original, but the diagnostic tool displayed "configuration mismatch". Using VDS, the technician performed "SRS system configuration", entering the correct VIN and configuration code (confirming side curtain airbag presence and quantity). Writing the settings to the ECU cleared the fault. The system recognized the airbag as absent because the ECU replacement did not include the required software configuration.
BYD DTC AI Analysis

BYD Qin EV: Wiring harness not restored after A-pillar repair causes open circuit

✓
2019 Qin EV. Minor left-front collision; repaired at non-authorized shop. Months later, DTC B17601B set. Inspection found the left front curtain airbag harness had been accidentally cut during A-pillar bodywork and simply twisted together instead of repaired with dedicated waterproof connectors. The wiring oxidized and opened. Re-soldered the harness and sealed with heat-shrink tubing. Resistance returned to normal; fault cleared. Airbag harnesses require OEM-standard repair procedures. Simple twist splices are prohibited.
BYD DTC AI Analysis

Clock spring fractured inside BYD E2 airbag module

✓
An E2 suddenly set DTC B17601B during normal use. Checked wiring harness and connectors—all normal. Measured infinite resistance between airbag module terminals; confirmed internal squib spiral cable fractured. Replaced left front side curtain airbag module (Note: replace headliner simultaneously or remove carefully). Calibrated system after replacement. Teardown revealed internal flat cable fractured from long-term folding fatigue—early component quality failure.
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.