AU
B16C8

DTC B16C8 indicates a functional fault or internal self-check abnormality in the airbag control unit (SRS ECU) — Seal U

Safety System

DTC B16C8 indicates a functional fault or internal self-check abnormality in the airbag control unit (SRS ECU).

As the core control module of the passive safety system, this ECU integrates longitudinal/lateral acceleration sensors, safety sensors, and a microprocessor.

It monitors real-time vehicle collision status, calculates collision severity, and controls the ignition and deployment timing of protective devices such as airbags, seat belt pretensioners, and knee airbags.

The following conditions trigger this DTC: internal ECU processor faults (such as a damaged Freescale/NXP main control chip), EEPROM data checksum failures, power management circuit abnormalities, internal safety monitoring circuit protection events, or communication interruptions between the ECU and the vehicle CAN network.

When this fault occurs, the SRS system enters fail-safe mode and the airbag warning lamp illuminates continuously.

In extreme cases, the airbags may fail to deploy during a collision or deploy unintentionally while driving due to false detection, posing a severe safety hazard.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: Damaged main control chip (MCU), corrupted internal memory (Flash/EEPROM) data, or failed power management IC (PMIC), causing the ECU to fail the Power-on Self Test.
  • 2Power supply system fault: Blown constant power (+B) circuit fuse (usually a 10A or 15A dedicated SRS fuse), excessive relay contact resistance, or ignition switch power (IG1/IG2) voltage fluctuations (below 9V or above 16V), causing ECU power instability or reset.
  • 3Ground circuit fault: SRS ECU ground point (usually G101 on the left instrument panel frame or the lower center console ground point) is loose, oxidized, corroded, or has uncleaned paint, causing excessive ground resistance (>1Ω) and affecting sensor signal reference voltage stability.
  • 4CAN communication bus fault: Open circuit, short to ground, or short to power in the CAN_H/CAN_L lines between the SRS ECU and the Gateway or Vehicle Control Unit (VCU), or abnormal terminating resistance (powertrain CAN standard 60 Ω, single ECU internal resistance 120 Ω), causing a communication timeout between the ECU and the vehicle network.
  • 5External factors causing ECU damage: Water ingress into the ECU mounting compartment (located in the lower centre console or behind the glovebox) after vehicle wading causes PCB corrosion and solder joint short circuits; or excessive impact acceleration (over 50g) during a collision physically damages the internal sensors.
What To Do
  • 1
    Use the VDS2000/VDS3000 diagnostic tool to access the SRS system. Read the complete DTC list and freeze frame data. Check for accompanying fault codes such as B16C7 (SRS_ECU internal fault) and U0140 (lost communication with BCM). Record key information at the time of the fault, such as vehicle speed and ignition cycle count.
  • 2
    Check the SRS ECU power supply system: disconnect the battery negative terminal, wait 3 minutes, and disconnect the ECU connector. Measure the voltage to ground at ECU connector terminal 1 (+B constant power) and terminal 2 (IG power); the standard value is 11-14V. Check if the SRS fuse in the engine compartment or dashboard fuse box (labelled 'SRS' or 'AIR BAG') is blown. Measure the resistance between the ECU ground terminal and body ground; the resistance must be less than 1 Ω.
  • 3
    Check the CAN communication circuit: Disconnect the ECU connector and use a multimeter to measure the CAN_H to ground voltage (approximately 2.6–3.0 V), the CAN_L to ground voltage (approximately 2.0–2.4 V), and the resistance between CAN_H and CAN_L (60 ± 5 Ω with power off; 120 Ω if measuring the ECU-side terminal resistance separately). Use an oscilloscope to check the CAN waveform for abnormal interference.
  • 4
    Inspect the SRS ECU connector and wiring harness: Check the 32-pin or 48-pin connector (depending on vehicle model) for backed-out pins, pin corrosion, and wiring harness damage. Particularly for vehicles driven through water, inspect the ECU mounting compartment for signs of water ingress. Verify sealing ring integrity. If necessary, clean with electrical contact cleaner and spray WD-40 for protection.
  • 5
    Perform the SRS ECU self-test and wiring harness wiggle test: After clearing the fault code, cycle the ignition 3 times (ON-OFF interval 5 seconds). Perform a road test or simulated vibration test and observe if the fault code returns. If the fault is intermittent, specifically inspect the instrument panel wiring harness retaining clips at the steering column and A-pillar for wear causing an intermittent short circuit.
  • 6
    SRS ECU replacement and programming: If wiring measurements are normal and the fault code persists, replace the airbag control unit. After installing the new ECU, use VDS to perform "SRS ECU Programming", write the vehicle VIN and Configuration Code (based on specific vehicle configurations such as airbag quantity and seat type), and perform "Crash Sensor Calibration" (Calibration).
  • 7
    System function verification: After repair, use the diagnostic tool to read the data stream of all SRS-related modules (side airbag sensors, front crash sensors, seat belt pretensioners, etc.) and confirm no abnormalities. Perform a simulated crash test (using a dedicated SRS tester) or an 'active test' (if available). Verify the airbag warning light turns off normally after the 6-second self-check and the system status displays as 'Normal'.
Real-World Cases
BYD DTC AI Analysis

Loose SRS ECU power supply connection on BYD Tang DM causes intermittent B16C8 fault

✓
Model: 2021 Tang DM. Symptoms: The dashboard airbag warning light illuminates intermittently; frequency increases on bumpy roads. DTC B16C8 status alternates between current and history. Diagnosis: Scanned with VDS, retrieved DTC B16C8-00. Measured SRS ECU power supply and found a 0.3–0.8 V voltage drop at the constant power terminal of the ECU connector. Traced the fault to the SRS fuse (15A) socket below the engine compartment fuse box. Internal spring tabs had fatigued and loosened; vehicle vibration increased contact resistance, causing momentary ECU power loss and reset. Repair: Replaced the fuse socket and fuse. Repaired the wiring harness terminal using dedicated crimping pliers. Applied conductive paste, reconnected, and completely resolved the fault.
BYD DTC AI Analysis

Water ingress caused internal corrosion damage to the SRS ECU on a BYD Yuan EV.

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Vehicle: 2019 BYD Yuan EV535. Symptoms: After driving through floodwater during heavy rain, the instrument cluster displayed 'Check SRS System', the airbag warning light stayed on, and the scan tool read DTC B16C8 (could not be cleared) along with B16C7 (internal fault). Diagnosis: Removed the SRS ECU located beneath the centre console, to the right of the blower motor. The housing seal gasket was aged and damaged, the internal PCB showed obvious water staining and electrolytic corrosion, and the power regulator chip (LDO) had a shorted output. Repair: Replaced the SRS ECU with a new unit (part no. E5A-5823010A). Used VDS2000 to write the VIN and configuration code (5-airbag configuration). Dried the cabin floor and replaced the sealing foam on the ECU mounting bracket.
BYD DTC AI Analysis

CAN bus fault on BYD Song MAX caused loss of communication with SRS ECU

✓
Model: 2019 Song MAX. Symptom: Airbag warning light came on suddenly during normal driving. The scan tool showed DTCs B16C8 and U0140 (lost communication with BCM). Diagnosis: Measured pins 6 (CAN_H) and 14 (CAN_L) at the OBD diagnostic port and found CAN_H shorted to ground (0V). Traced the fault to the dashboard wiring harness at the steering column mounting bracket where long-term chafing had damaged the insulation, causing the CAN_H wire to short against the metal bracket. This interrupted communication between the SRS ECU and the vehicle network, triggering the fault codes. Repair: Repaired the damaged wiring using double-layer heat shrink tubing, rerouted the harness and added anti-chafe sleeving. Cleared the fault codes and the SRS system communication returned to normal.
BYD DTC AI Analysis

After an accident repair, an SRS ECU configuration error on a BYD Qin Pro caused B16C8.

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Vehicle: 2020 Qin Pro petrol. Symptoms: Following front collision repairs, replaced the SRS ECU with a new unit, but the airbag warning light stays on, logging DTC B16C8 which will not clear. Diagnosis: New ECU hardware installation correct, power and ground circuits normal. VDS shows 'System Configuration Status' as 'Not Configured'. The new ECU lacks the vehicle-specific configuration code (this variant has 4 airbags: dual front and side, requiring a specific hexadecimal value). Repair: Accessed the 'SRS System Configuration' function using VDS, retrieved and wrote the correct configuration code (0x4A2B) based on the VIN, then performed seat position sensor calibration. The warning light went out and the system returned to normal operation.
BYD DTC AI Analysis

Poor SRS ground on BYD Yuan EV after battery pack repair

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Model: 2019 Yuan EV. Symptoms: After the dealership removed and reinstalled the battery pack, the vehicle immediately logged DTC B16C8 on power-up, along with multiple sensor communication faults. Diagnosis: To remove the instrument panel assembly, the tech removed the SRS ECU ground bolt. When reinstalling, the tech did not torque the bolt (located on the instrument panel bracket under the left A-pillar) to spec, and did not clean the paint from the ground point. This caused the ground resistance to measure 8Ω (spec <1Ω), leading to ECU ground potential drift. Repair: Cleaned the ground point to bare metal, applied conductive paste, and torqued the ground bolt to the workshop manual spec of 10 N·m. Ground resistance measured 0.3Ω afterwards. Fault codes cleared, no 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.