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B1602

DTC B1602 indicates a short to power in the driver frontal airbag (DAB) igniter circuit — Seal U

Safety System

DTC B1602 indicates a short to power in the driver frontal airbag (DAB) igniter circuit.

In the BYD SRS (Supplemental Restraint System) architecture, the Airbag Control Unit (ACU) continuously monitors the circuit resistance of each airbag igniter (normally about 2-3 Ω) and its insulation status.

When the ACU detects abnormal continuity between the driver airbag igniter wiring and the vehicle power supply (12V+) (resistance below the threshold, typically <10 kΩ for a short to power), it triggers this fault.

This fault means the airbag may deploy unexpectedly while driving (a serious safety risk) or fail to deploy properly in a collision because the power supply clamps the circuit.

The fault may originate in the clock spring (spiral cable), airbag wiring harness, connector, or the ACU internal driver circuit.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Clock spring internal damage: Frequent steering wheel rotation wears and breaks the internal ribbon cable, causing the wire to short circuit against the power cable. Common on high-mileage BYD Tang and Song series vehicles.
  • 2Airbag wiring harness insulation damaged: The wiring harness below the steering wheel rubs inside the steering column, sharp edges cut the harness, or improper securing after accident repairs causes the harness to contact a 12V power wire (such as the horn circuit or multifunction switch power supply).
  • 3Water ingress or liquid corrosion: A/C condensate leakage or poor front windshield sealing allows water to flow beneath the steering wheel, corroding the airbag connector terminals (usually the yellow plug) and causing a short circuit between terminals or a short to power.
  • 4Non-OEM modifications: Improper handling when installing steering wheel buttons, modifying the push-to-start system, or wrapping the steering wheel in leather damages the airbag wiring harness or introduces external power interference.
  • 5Airbag Control Unit (ACU) internal fault: ACU internal ignition driver chip breakdown (MOSFET short circuit) causes the output terminal to continuously output supply voltage. Replace the ACU assembly and reconfigure the coding.
What To Do
  • 1
    Safety Preparation: Turn the vehicle OFF, disconnect the 12V battery negative terminal, and wait at least 90 seconds (to ensure the SRS capacitor fully discharges and prevent accidental airbag deployment). Wear an anti-static wrist strap. Do not use non-explosion-proof testing equipment near the airbag.
  • 2
    Visual inspection: Check the yellow airbag connector below the steering wheel (usually on the left side of the steering column) for oxidation or water ingress; check the clock spring connector for looseness and bent pins; check the steering wheel for signs of modification.
  • 3
    Circuit measurement: Set the multimeter to the resistance range (verify the multimeter has no voltage output). Disconnect the connection between the vehicle body and the airbag. Individually measure the resistance between the airbag-side wiring harness and the body power supply (must be >1 MΩ). Test the ACU-side wiring harness for a short circuit to the power supply.
  • 4
    Component isolation test: Remove the driver airbag (disconnect the upper end of the clock spring) and measure the airbag module resistance (normal: 2.0-3.0 Ω). Connect an airbag simulator to the ACU side in place of the actual airbag. If the DTC clears, the clock spring or wiring harness is faulty. If the DTC remains, the ACU or chassis wiring harness is faulty.
  • 5
    Clock spring inspection: Remove the clock spring and visually inspect the internal ribbon cable for breaks or burn marks. Measure the continuity and insulation of each clock spring circuit. Replace the clock spring if testing indicates an open or short circuit. (Note: Some BYD models require matching the clock spring to the steering angle sensor; calibrate after replacement.)
  • 6
    Wiring harness repair: If the wiring harness is damaged, wrap it with high-temperature insulating tape (Tesa 51036 or equivalent) and reroute the harness to prevent contact with metal edges. If water has entered the connector, clean it with electronic contact cleaner, blow it dry, and apply conductive grease.
  • 7
    System reset: After repair, reconnect all components and the battery. Use the VDS or Launch X-431 diagnostic tool to access the SRS system and execute 'Clear DTCs' and 'System Self-test'. Confirm B1602 becomes a history code or clears. Verify the SRS warning lamp turns off after the self-test.
  • 8
    Function verification: Perform an ignition cycle test (ON-OFF three times) and confirm the fault code does not return. Perform an airbag system communication test and confirm normal communication between the ACU and all sensors.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Worn clock spring caused B1602 in BYD Tang DM

✓
2021 BYD Tang DM, 80,000 km. SRS warning light stays on constantly. Retrieved DTC B1602 (driver airbag short to power). Disassembly revealed the clock spring’s internal ribbon cable had fractured due to long-term rotational fatigue. The broken copper wire at the fracture point made contact with the metal frame, causing a short to power. Replaced with genuine clock spring (part number: SC-3636100); fault cleared. Note: The Tang series clock spring integrates the steering angle sensor. After replacement, use a diagnostic tool to perform ‘steering angle sensor calibration’; otherwise the ESP system will set a fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song MAX airbag wiring harness corroded after wading.

✓
2019 BYD Song MAX. After wading through deep water during a heavy rainstorm, the instrument cluster displayed 'Check SRS System'. The scan tool reported DTC B1602. Inspection found the driver's side A-pillar drain hole blocked. Water entered along the dashboard and pooled under the steering wheel, causing the yellow 2-pin airbag connector (C202) terminals to oxidize and develop verdigris, shorting the power and signal terminals. Repair: cleaned the connector terminals with WD-40 Specialist Electrical Contact Cleaner, replaced the waterproof seal, cleared the drain hole, and re-wrapped the wiring harness. Fault has not recurred.
BYD DTC AI AnalysisFrom Chinese market (translated)

Steering wheel modification triggered fault in BYD Yuan EV

✓
2019 BYD Yuan EV535. Owner retrofitted a multi-function steering wheel. A B1602 DTC appeared the next day. Inspection found that a screw had pierced the steering wheel wiring harness protective sleeve during the modification. The puncture point touched the steering wheel frame (body ground is actually the 12V circuit after the load), creating a short to power. Repair: Replaced the damaged airbag wiring harness (including the upper clock spring section), rerouted the wiring according to specifications, and used dedicated harness clips to prevent metal contact. Note: BYD airbag systems are sensitive to circuit impedance; non-professional modifications can easily trigger faults.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro: ACU Internal Fault Misdiagnosis Case

✓
2020 BYD Qin Pro (petrol variant). DTC B1602 appeared repeatedly. After replacing the clock spring and airbag, the fault recurred intermittently. Further inspection found that pin 3 of the ACU internal firing driver chip (NXP MC33797) had shorted to the power supply, causing continuous 12V output to the driver airbag circuit. External measurements can't detect this internal short; you need an oscilloscope to capture abnormal waveforms during the ACU self-test. Finally, replacing the airbag control module (located under the centre console, part number E5A-3658100) and performing module coding and crash data reset resolved the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song Pro wiring harness unsecured after accident repair

✓
2021 BYD Song Pro. B1602 triggered three months after front-end accident repairs. Investigation traced the fault to the repair process. During reassembly of the steering wheel and dashboard, the technician failed to clip the airbag harness into the steering column retaining clip. The unclipped harness chafed against the dashboard metal bracket when the steering column turned, eventually wearing through the insulation and shorting to constant power (horn supply wire, orange). Repair: Soldered the damaged conductors and sealed with heat-shrink tubing, restored the harness to the original retaining clip positions, and adjusted harness slack. Note: BYD workshop manuals require airbag harnesses to be secured with original clips and maintain at least 50 mm clearance from the body.
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]