AU
B16C3-00

BYD strictly defines B16C3-00 as an open circuit or excessive resistance fault in the driver airbag (DAB) stage 1 ignition circuit — Seal U

Safety System

BYD strictly defines B16C3-00 as an open circuit or excessive resistance fault in the driver airbag (DAB) stage 1 ignition circuit.

Although the original description states "SRS_ECU fault", it actually indicates a communication or circuit anomaly between the driver airbag module and the SRS control unit, rather than an ECU hardware failure.

This fault indicates the airbag control module (ACM) detects the driver-side airbag ignition circuit resistance falls outside the normal range (standard value 2.0±0.1Ω).

This typically presents as infinite resistance (open circuit) or greater than 5Ω (poor connection).

When this fault activates, the airbag system enters fail-safe mode, the driver-side airbag will not deploy during a collision, and the instrument cluster SRS warning light remains illuminated.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Clock spring internal flat cable broken or has poor contact: Long-term steering wheel rotation causes fatigue fracture of the internal flexible circuit. This is the most common cause.
  • 2Poor contact at the airbag wiring harness connector: Includes oxidation or looseness of the yellow connector under the steering wheel, or the shorting bar (short-circuit tab) failing to fully return, causing an open circuit.
  • 3Wiring harness mechanical damage: A broken harness retaining clip below the steering wheel causes the harness to rub against the steering column, breaking the internal copper wires; or sharp edges cut or crush the harness during repairs.
  • 4Excessive twisting of the clock spring lower wiring harness: Failing to align the steering wheel correctly after removal and installation causes excessive internal winding and damages the clock spring.
  • 5Internal ignition driver circuit fault in the SRS control unit (very rare): A damaged internal MOSFET or boost circuit in the control module fails to detect normal resistance.
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the 12V battery negative terminal, and wait at least 3 minutes to fully discharge the SRS system energy storage capacitor and prevent accidental airbag deployment.
  • 2
    Fault code reading: Use a VDS2000 or Launch X-431 diagnostic tool to access the SRS system, read the current fault codes and data stream, and verify the DAB circuit resistance (normal: 2-3 Ω).
  • 3
    Visual inspection: Check the SRS warning light status on the instrument panel, inspect the yellow airbag connector under the steering wheel for oxidation or looseness, and verify the shorting bar has returned to its normal position.
  • 4
    Clock spring inspection: Remove the driver-side airbag module (use the special tool; never use a screwdriver). Gently turn the steering wheel and observe if the resistance value in the diagnostic tool data stream fluctuates. Measure continuity from the inner ring to the outer ring of the clock spring.
  • 5
    Wiring harness continuity check: Check the securing condition of the wiring harness below the clock spring. Strip the harness insulation and check for internal breaks or broken copper strands. Check the wiring harness for interference or wear against the steering column or metal bracket.
  • 6
    Resistance measurement specification: Never use a multimeter to directly measure airbag resistance (may trigger accidental deployment). Read resistance values only via the diagnostic tool data stream. To measure circuit continuity, disconnect the airbag module connector.
  • 7
    Component replacement: If the clock spring has an internal open circuit, replace it with an OEM clock spring assembly (align to the center position during installation). If the wiring harness is damaged, cut out the damaged section, resolder, and repair using the dedicated yellow wiring harness. Keep the shielding layer intact.
  • 8
    System reset: Reconnect all connectors (listen for the locking clip click), connect the battery, use the diagnostic tool to perform the 'SRS System Configuration' or 'Sensor Calibration' procedure, and clear the fault code.
  • 9
    Function verification: Perform an SRS system self-check ignition cycle test. Confirm the DAB circuit resistance returns to the 2.0-2.5 Ω range and the SRS warning lamp turns off normally. Road test the vehicle for verification (including turning the steering wheel and driving on bumpy roads).
Real-World Cases
BYD DTC AI Analysis

Clock spring oxidation causing SRS warning light to stay on in Qin Pro DM

✓
2019 BYD Qin Pro DM with 42,000 km. SRS warning light stays on after starting. Scan tool reads DTC B16C3-00; live data shows infinite driver airbag resistance. Disassembly found an oxidised yellow connector at the base of the clock spring and an intermittent internal open circuit. Replaced the steering wheel clock spring (EF-4123100), cleaned the oxidised terminals, and applied conductive grease. Fault cleared, resistance returned to 2.4Ω.
Original source ↗
BYD DTC AI Analysis

Steering wheel removal and refitting on Song MAX: connector shorting bridge not returned to position.

✓
2020 BYD Song MAX 1.5T. SRS warning light came on suddenly while driving. Earlier, a dash cam installation involved removing and reinstalling the steering wheel. Diagnostics showed DTC B16C3-00: Driver airbag first stage ignition circuit fault. Inspection found the airbag connector shorting bar had not fully returned, and that work had caused a harness connector pin to back out. Repaired the pin, confirmed the shorting bar worked correctly, performed airbag configuration, and cleared the fault codes. A 50 km road test confirmed the fault did not return.
Original source ↗
BYD DTC AI Analysis

Tang DM clock spring intermittent connection causing intermittent alarm

✓
2021 Tang DM High-Performance AWD, 8500 km. SRS warning light would occasionally come on during cold starts, sometimes go out on its own once warm, and later stay on permanently. VDS2000 detected DTC B16C3-00; fault history indicated high resistance. DAB circuit resistance fluctuated between 5 and 10 Ω. Inspection found the clock spring's internal flat cable had an intermittent connection; resistance jumped when turning the steering wheel. Replaced the clock spring assembly under warranty (part no. 5EF-4123100). Performed the self-test procedure; fault resolved.
Original source ↗
BYD DTC AI Analysis

Wiring harness chafing caused intermittent open circuit in e5 taxi.

✓
2018 BYD e5 450 taxi, 180,000 km. The SRS warning light came on intermittently, usually when turning the steering wheel or driving on bumpy roads. Autel MS906BT retrieved DTC B16C3-00. Inspection found the wiring harness retaining clip beneath the clock spring had fractured, allowing the harness to chafe against the steering column over time. The yellow signal wire had broken internal copper strands, with only minimal contact remaining. Repaired the damaged harness by soldering, insulating, and shielding the wire. Re-secured the harness and fitted an abrasion-resistant sleeve. Also installed a used OEM clock spring. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Han EV wiring harness pinched after collision repair causing short-to-open circuit

✓
2020 Han EV Ultra-Long Range. SRS warning light stayed on after minor front collision repairs. Front bumper and left fender previously replaced. Read DTCs: B16C3-00 (current) and B1650-00 (history). Found the technician had pinched the driver airbag wiring harness during dashboard removal, damaging the insulation and causing a short circuit; an improper repair then created an open circuit with infinite resistance. Replaced the damaged wiring section using OEM yellow dedicated wiring, rerouted the harness clear of sharp metal edges, cleared the codes and performed an ignition cycle test. DAB circuit resistance restored to 2.3Ω, system normal.
Original source ↗
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.