AU
B16C2

DTC B16C2 indicates an internal hardware or software self-test failure in the airbag control unit (SRS ECU) — Seal U

Safety System

DTC B16C2 indicates an internal hardware or software self-test failure in the airbag control unit (SRS ECU).

This fault signifies a functional failure in the ECU internal microprocessor, EEPROM memory, crash sensor interface circuit, or firing circuit driver.

The ECU performs internal diagnostics at each power-up.

If the ECU detects a CPU calculation error, memory checksum failure, internal communication bus fault, or firing circuit driver chip abnormality, it sets this DTC and enters fail-safe mode.

The airbag system completely disables, and the airbags may fail to deploy during a collision.

This condition also affects related systems such as the seat belt pretensioners and airbag warning lamp.

This constitutes a hard fault and typically will not clear by simply disconnecting power.

Replace the ECU or repair the internal hardware.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Hardware damage to the SRS ECU internal processor or memory chip, typically due to voltage surges or component aging.
  • 2Abnormal ECU power supply voltage (below 9V or above 16V) causes unstable internal circuit operation or reset.
  • 3Poor contact, oxidation, or high resistance in the ECU ground circuit, causing signal reference potential drift.
  • 4Vehicle wading, high-humidity environments, or improper car washing causes ECU seal failure, resulting in internal circuit board corrosion and short circuits.
  • 5Corrupted ECU software or crash calibration data, possibly due to improper power disconnection or electromagnetic interference.
What To Do
  • 1
    Use a dedicated diagnostic tool (such as BYD ED400 or VDS) to read the full fault codes. Confirm B16C2 is a current fault and freeze frame data shows it triggered during the ECU self-check phase. Clear the fault code, power on again, and observe whether the fault reoccurs.
  • 2
    Check the SRS ECU housing ground point (usually located on the center tunnel or instrument panel frame). Remove the ground bolt and clean the contact surfaces. Measure the ground resistance; it must be less than 1Ω. Verify the connection is free of oxidation or paint.
  • 3
    Disconnect the SRS ECU main wiring harness connector (e.g., G36/G37). Measure the voltage at the harness-side power supply terminals (constant +B and IG power). The voltage should be 9-16V. Measure the CAN-H (approx. 2.5-3.5V) and CAN-L (approx. 1.5-2.5V) line voltages and the terminal resistance (approx. 60Ω).
  • 4
    Visually inspect the ECU connector pins for backed-out pins, corrosion, signs of water ingress, or pin spread. Clean the connector with electrical contact cleaner. Repair or replace the wiring harness terminals if necessary. Verify the waterproof sealing ring is intact.
  • 5
    If circuit measurements are normal, attempt an SRS ECU software upgrade or calibration data refresh. If the fault persists, diagnose an internal ECU hardware fault and replace the SRS ECU assembly (verify the part number based on the vehicle model, e.g., Yuan EV: ED-5820100).
  • 6
    After replacing the ECU, perform online configuration coding (VIN writing and vehicle model configuration), collision sensor zero-point calibration, and a system self-check. Confirm the fault code clears and the instrument cluster airbag warning lamp turns off normally (turns off 6 seconds after power-on).
Real-World Cases
BYD DTC AI Analysis

BYD Qin Pro SRS ECU internal processor fault

✓
Instrument panel airbag warning light stayed on constantly. Retrieved DTC B16C2 (active fault). Checked ECU supply voltage: 12.4V – normal. Earth resistance: 0.3Ω – normal. CAN communication waveform: normal. Disconnected power for 30 minutes and cleared the fault code. The DTC returned immediately upon power-up. Disassembled the SRS ECU; internal circuit board showed no signs of water ingress, but the main control chip showed signs of heat discolouration. Replaced the SRS ECU (part number ED-5820100A), performed system calibration and coding. This resolved the fault, and the airbag warning light went out normally.
Original source ↗
BYD DTC AI Analysis

BYD Song MAX wiring harness pin backed out causing intermittent fault

✓
The airbag warning light occasionally illuminated on rough roads and sometimes cleared after switching off and restarting. The diagnostic tool read DTC B16C2 as an intermittent fault. Inspection of the SRS ECU connector G36 found pin 35 (earth) had backed out by approximately 2 mm, causing an intermittent earth connection while driving. Repaired the terminal by re-crimping and fully seating it, then reinforced the wiring harness fixing point with special waterproof tape. Road tested for 30 km with no recurrence; fault fully resolved.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM ECU internal corrosion after wading

✓
After driving through water approximately 40 cm deep, the instrument cluster displayed an airbag warning. DTC B16C2 was present and could not be cleared. Removed the SRS ECU (located beneath the centre armrest console) and found the outer seal had deteriorated, with visible water staining and pin corrosion on the internal circuit board. Measured a short circuit in the ECU's internal voltage regulation circuit. Replaced the SRS ECU along with the wiring harness waterproof connectors. Added a waterproof cover to the mounting location. Fault cleared. Recommend inspecting the ECU seal on vehicles from the same production batch.
BYD DTC AI Analysis

BYD Yuan EV voltage instability caused ECU damage

✓
After fitting a high-power audio system, the airbag warning light came on frequently. Diagnosis showed DTC B16C2. Inspection found the aftermarket wiring had tapped directly into the SRS ECU power circuit, causing voltage to drop to 7.2V at startup. This caused the ECU to reset repeatedly, damaging the internal memory. Removed the unauthorized wiring and restored the factory wiring layout; replaced the damaged SRS ECU; advised the customer not to tap power from the SRS system. A one-month follow-up confirmed no fault recurrence.
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.