AU
B16C4-00

B16C4-00 indicates the airbag control unit (SRS ECU) detects an internal fault or critical communication anomaly — Atto 8

Safety System

B16C4-00 indicates the airbag control unit (SRS ECU) detects an internal fault or critical communication anomaly.

This fault code indicates the ECU self-diagnostic detected an error in the processor, memory, power supply monitoring circuit, or internal safety logic, or the ECU lost communication with the crash sensors or airbag modules.

Because the SRS ECU is the core of the passive safety system, this fault causes the airbag system to enter fail-safe mode.

During a collision, the front, side curtain, or knee airbags may fail to deploy, and the seat belt pretensioners may also fail.

When this fault triggers, the ECU typically cuts power to the airbag ignition circuits to prevent inadvertent deployment.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1SRS ECU internal hardware damage (main control chip, EEPROM memory, or power voltage regulator module failure, commonly caused by water ingress or prolonged high-temperature exposure)
  • 2Power supply system fault (blown fuse F1/14, poor connection in IG1/IG2 power supply circuit, or ECU protective lockout due to battery voltage below 9V or above 16V)
  • 3Ground circuit fault (loose or oxidized G301 ground point, or broken wiring harness, causing ECU reference voltage drift)
  • 4CAN bus communication fault (short circuit between CAN-H and CAN-L, short to ground, abnormal line resistance (not 60Ω), or electromagnetic interference causing data frame errors)
  • 5Crash sensor circuit short (damaged front or side crash sensor wiring harness causes a short, triggering internal ECU fault protection mechanism)
What To Do
  • 1
    Safety preparation: Disconnect the low-voltage battery negative terminal, wait at least 90 seconds for the SRS capacitor to fully discharge, and wear an anti-static wrist strap.
  • 2
    Diagnostic scan: Use VDS2000 or Launch X431 to read all fault codes, check for B16C4-00 and any accompanying sensor communication fault codes, and record freeze frame data.
  • 3
    Visual inspection: Check the SRS ECU housing (usually located beneath the center console or in front of the gear selector) for water stains, burning, or impact marks. Check connectors KJB-1 and KJB-2 for oxidation or backed-out pins.
  • 4
    Power and ground measurement: Reconnect the battery. Measure the ECU connector: pin 1 (constant B+) voltage should be 12V, pin 2 (IGN) voltage should be 12V with the ignition switch ON, and pin 3 ground resistance should be less than 1Ω.
  • 5
    CAN bus check: Measure the static voltages of CAN-H (approx. 2.6V) and CAN-L (approx. 2.4V). Use an oscilloscope to verify a regular waveform. Measure the terminating resistance; it should be approximately 60Ω.
  • 6
    Wiring harness continuity test: Disconnect the ECU from all crash sensors and airbag modules. Use a multimeter to measure the continuity and insulation resistance of each circuit to locate short or open circuits.
  • 7
    Software update: If the wiring is normal, use the latest diagnostic software to update the SRS ECU software or rewrite the calibration data (manufacturer authorization required).
  • 8
    Replacement and Matching: If the fault persists, replace the SRS ECU with the same model. Perform online coding, write the VIN, and configure the crash sensors. Clear the fault codes and perform a system self-test.
  • 9
    Function verification: Perform the airbag system self-test (the instrument panel airbag warning lamp should illuminate for 6 seconds, then turn off). Use a diagnostic tool to read the sensor data stream and perform a simulated crash test (if supported).
Real-World Cases
BYD DTC AI Analysis

Qin EV300 dashboard airbag warning light stays on with DTC B16C4-00

✓
After the vehicle waded through water, the dashboard airbag warning light remained illuminated. The scan tool retrieved DTC B16C4-00 and multiple sensor communication faults. Disassembly revealed water staining at the SRS ECU mounting location (below the centre console). The ECU housing seal had deteriorated, allowing water to enter. The ECU internal power supply module showed a short to ground. Replaced the SRS ECU, treated water staining on the wiring harness, and resealed the mounting location. Fault resolved.
BYD DTC AI Analysis

Qin 80 intermittently reports SRS ECU fault

✓
The airbag warning light occasionally flickers when driving on rough roads but operates normally when stationary. Retrieved historical DTC B16C4-00. Found the G301 ground point bolt (below the left A-pillar) loose, causing a poor ground connection and unstable ECU operating voltage. Resurfaced the ground point, tightened the bolt to 8 N·m, and applied conductive anti-corrosion compound. The fault has not recurred.
BYD DTC AI Analysis

Battery replacement triggered SRS ECU fault

✓
The airbag warning light stayed on after replacing the battery. The diagnostic scan showed fault code B16C4-00. During the repair, a tool accidentally shorted SRS fuse F1/14, causing an abnormal ECU reset. The fault remained after replacing the fuse. The ECU lost its internal memory data. Reflashing the ECU software and reconfiguring the sensor parameters fixed the issue.
BYD DTC AI Analysis

CAN bus interference caused SRS system failure

✓
After installing an aftermarket dashcam, the SRS warning light came on. The diagnostic scanner showed code B16C4-00 and communication timeout faults. Inspection found the dashcam was drawing power from the SRS ECU ignition supply, and a poor connection at the CAN bus splitter caused signal reflection. Removed the unauthorised wiring, repaired the CAN bus termination resistor, and cleared the fault codes. System now operating normally.
BYD DTC AI Analysis

Crash sensor short circuit triggered ECU protection

✓
After a minor front-end collision, the airbags did not deploy but the warning light illuminated. Retrieved DTC B16C4-00 for a left front impact sensor short circuit fault. Inspection found the accident had crushed and damaged the sensor wiring harness, causing a short between positive and negative that burnt out the ECU's internal protection circuit. After repairing the harness and replacing the left front impact sensor, the SRS ECU also required replacement (internal protection circuit damaged). Completed online matching; fault resolved.
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.