AU
B16C1

DTC B16C1 indicates the airbag control unit (SRS ECU) detected an internal system fault or an external power supply or communication abnormality — Atto 8

Safety System

DTC B16C1 indicates the airbag control unit (SRS ECU) detected an internal system fault or an external power supply or communication abnormality.

Specifically, this code points to a functional failure in the ECU power management module, internal memory (EEPROM/Flash) self-check, watchdog timer, or main processor.

The SRS ECU triggers this fault code and illuminates the airbag warning lamp if it detects an operating voltage outside the 9-16V range, an internal data verification failure, or a loss of communication with the vehicle CAN network during the ignition cycle self-check.

This fault forces the airbag system into a degraded mode.

During a collision, the system may fail to deploy the airbags or actuate the seatbelt pretensioners, posing a severe safety hazard.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Low-voltage battery discharged or voltage unstable (extended parking causes voltage to drop below 9V, or a charging system fault causes voltage to exceed 16V), exceeding the normal operating voltage range of the SRS ECU.
  • 2SRS ECU power supply circuit fault, including a blown dedicated airbag fuse in the instrument panel fuse box (usually 10A or 15A), a backed-out power supply pin, or a poor circuit connection causing excessive voltage drop.
  • 3Abnormal ECU ground circuit resistance. Oxidation, excessive paint, or loose fastening bolts at the front bulkhead or instrument panel crossmember ground point cause the ground resistance to exceed 1Ω.
  • 4CAN bus communication fault: Short circuit between CAN-H and CAN-L lines, short to power or ground, or abnormal terminating resistor (usually 120Ω) prevents ECU communication with the vehicle gateway.
  • 5Internal hardware damage in the SRS ECU, including aging of the internal step-down capacitor, cold solder joints on the main control chip (MCU), or memory data corruption (reflash calibration data or replace the ECU)
What To Do
  • 1
    Pre-inspection and voltage measurement: Check the low-voltage battery voltage. Standard value: 12.5-14.5V (ignition switch ON). If the voltage is abnormal, first rectify the battery or DC-DC fault, clear the DTC, and rerun the self-check.
  • 2
    Fault code reading and freeze frame analysis: Use a VDS or Launch diagnostic tool to read all DTCs. Check for accompanying U-class communication fault codes (such as U0100) or related codes like B16C0/B16C2. Record the freeze frame voltage values and mileage to determine if the fault is historical.
  • 3
    Power supply and ground circuit check: Disconnect the battery negative terminal, wait 90 seconds for the capacitor to discharge, then unplug the SRS ECU connector (typically a 39-pin or 54-pin black connector). Measure the voltage between connector terminal 1 (constant power B+) and body ground, and between terminal 2 (ignition power IG) and body ground (should be greater than 11V). Measure the resistance between the ground terminal and the body ground point (should be less than 1Ω).
  • 4
    CAN communication line check: Use an oscilloscope or multimeter to measure the resistance between CAN-H (orange/black) and CAN-L (orange/brown) at the SRS ECU connector (approximately 60Ω, two 120Ω terminating resistors in parallel), and measure insulation to ground and power supply.
  • 5
    Wiring harness and connector inspection: Inspect the ECU connector for water ingress, corrosion, spread terminals, or backed-out terminals. Inspect the wiring harness sleeve at the front bulkhead pass-through for damage. On accident-repaired vehicles, specifically check for crushed or cut wiring harnesses.
  • 6
    Replacement verification and calibration: If all wiring measurements are normal, replace the SRS ECU with one of the same part number (Note: BYD ECU part numbers differ between models; for example, do not interchange Yuan EV and Tang units). After replacement, perform online configuration (Coding) and airbag system calibration (Calibration). Some models require special equipment to write the VIN and configuration word.
  • 7
    System self-check and crash output test: After replacement, connect the diagnostic tool to clear the fault codes. Perform an ignition cycle self-check (IGN ON, wait 6 seconds, and verify the airbag warning lamp turns off). Perform the passive safety system function test (use a dedicated resistor substitute; never directly measure the airbag squib resistance). Confirm no fault codes remain before returning the vehicle.
Real-World Cases
BYD DTC AI Analysis

2019 BYD Song MAX: Flat battery caused intermittent B16C1 fault

✓
After sitting for 5 days, the vehicle displayed 'Check SRS System' on startup. Retrieved DTC B16C1. Battery voltage measured only 10.8V – discharged from sitting. Charged the battery to 12.6V, cleared the code, and the fault temporarily disappeared. Returned a week later. Measured static current draw at 180mA (should be under 50mA). Traced to parasitic drain from an aftermarket dashcam wired to constant power. Replaced the battery and fixed the drain; fault permanently resolved.
BYD DTC AI Analysis

2021 Tang: Poor SRS ECU grounding caused false system warnings

✓
The airbag warning light illuminated intermittently when driving on rough roads. Scanned the system and retrieved current DTC B16C1. Found the SRS ECU ground bolt (M6) loose at the dashboard crossmember. Improper cleaning left paint residue on the ground point, resulting in a measured resistance of 4.2Ω. Sanded the ground point to bare metal, applied conductive paste, and tightened the bolt to the specified torque (8-10 N·m). Ground resistance dropped to 0.3Ω. Road tested for 20 km with no fault recurrence. Returned vehicle to customer; no further issues after three months of use.
BYD DTC AI Analysis

2019 Yuan EV: B16C1 and U0151 present after accident repair

✓
After front collision repairs, the airbag warning light stayed on. DTCs read: B16C1 (SRS ECU fault) and U0151 (lost communication with airbag control unit). Inspection found the replacement bulkhead harness fitted during the collision repairs had terminals inside the new SRS ECU plug (39-pin) that weren't fully seated, causing poor contact on the CAN-H line (orange/black). Reseated the terminals, applied waterproof sealant, then performed 'Airbag System Configuration' and 'Collision Output Reset' using VDS. The DTCs cleared and the airbag light went out.
BYD DTC AI Analysis

BYD Qin Pro Petrol: SRS ECU Internal Failure Replacement Case

✓
While driving normally, an alarm went off and the airbag warning light stayed on. Could not clear DTC B16C1. Checked power, ground, and CAN lines — all normal. Measured ECU connector voltage: 12.4V; ground resistance: 0.5Ω; CAN waveform normal. Diagnosed an internal hardware fault in the SRS ECU. Replaced the ECU with a new unit (part no. BYD-3638100-XS2). Using the dedicated diagnostic tool, performed 'online configuration' (entered vehicle VIN to auto-download configuration data) and 'sensor calibration'. Then ran a simulated crash test (using a 2Ω resistor in place of the airbag). System worked normally, fault resolved.
BYD DTC AI Analysis

Yuan Pro 2021 — Outdated software version causes false alarm

✓
500 km after delivery, the SRS warning light came on, storing DTC B16C1. Checked wiring, no abnormalities found; voltage normal. Replacing the SRS ECU had no effect. Looked up BYD TSB-2021-SRS-03 and found that SRS ECU software version V1.02 in this production batch contains a bug—falsely reports internal faults under specific voltage fluctuations. Upgraded ECU software to V1.05 using VDS, with a backup battery connected to keep vehicle power stable. Cleared fault codes after the upgrade. Followed up for one month, no recurrence.
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.