B16C4
DTC B16C4 indicates an internal fault or severe communication failure in the airbag control unit (SRS ECU) — Atto 3
Safety System
DTC B16C4 indicates an internal fault or severe communication failure in the airbag control unit (SRS ECU).
This fault indicates a functional failure of the microprocessor, memory, or power management module within the SRS ECU, or a communication interruption between the ECU and the vehicle CAN network or sensor array.
The SRS ECU serves as the core controller of the passive safety system.
It receives crash sensor signals, determines collision severity, and triggers protective devices such as airbags and seat belt pretensioners.
This critical fault compromises occupant safety by potentially preventing normal airbag deployment during a collision, or by creating a risk of false alarms and unintended deployment.
When this fault occurs, the SRS system typically enters fail-safe mode, cuts off the airbag ignition circuit to prevent unintended deployment, and illuminates the instrument cluster airbag warning light.
Real-World Cases
BYD Qin/Tang series torque sensor main signal fault
**Symptoms:** While driving, the steering wheel suddenly got heavy and the EPS warning light came on the dashboard. Power steering assistance cut in and out, particularly at low speeds or when turning the wheel while stationary.
**Diagnosis:** Connected the VDS diagnostic tool and retrieved fault codes C1611 and C1612, related to the torque sensor. Battery voltage read normal. Measured 12.3V at pin 1 of the electric power steering control unit connector ER04. Disconnected the EPS control unit and torque sensor connectors and checked continuity between them. Found an open circuit between ER04 pin 3 and the torque sensor. Inspected the wiring harness routing and found the retaining clip under the steering wheel had come loose. Prolonged steering movement caused the internal copper wires to break.
**Resolution:** Repaired the broken wiring harness: resoldered the wires and applied insulation and waterproofing. Re-secured the harness retaining clip so the steering does not pull on the wiring. Cleared the fault codes and calibrated the torque sensor using dedicated equipment. Test drove the vehicle and confirmed the EPS function returned to normal.
Original source ↗BYD Song DM CAN network communication fault (including EPS-related)
Symptoms: The vehicle occasionally stalls while driving but restarts normally. When it stalls, the instrument cluster displays multiple warning lights including EPS, engine and transmission.
Diagnosis: Ran a VDS system scan. Found no current DTCs, but history records showed communication faults between the engine control unit (ECU) and transmission control unit (TCU). Deep-scanned the entire CAN network and found the electric power steering (EPS) control unit was intermittently dropping offline. Inspected the engine bay earth points and found the ECU earth bolt loose, with excessive contact resistance. Measured the EPS control unit supply voltage and found it dropped below 8.5V when the engine bay earth connection was poor.
Resolution: Retightened all earth bolts for the ECU and EPS control unit and applied conductive paste. Inspected and cleaned oxidation off the earth points, sanding them to bare metal. Checked power and earth connections for other CAN network modules and verified no loose joints. Road-tested for 20 km and confirmed the fault did not recur.
Original source ↗BYD Surui EPS steering angle sensor not calibrated
Symptoms: After replacing the steering column assembly, the steering wheel sits centred but the vehicle pulls to one side, the EPS warning light flashes, and steering assistance is asymmetric between left and right.
Diagnosis: Scanned for DTCs, which indicated 'steering angle sensor not calibrated' or signal abnormal. Inspected the steering column installation position and found the steering wheel was not fully centred during assembly. Used a diagnostic scan tool to read the steering angle data stream, which showed 15° with the steering wheel centred (normal range is 0±5°). Inspected the wiring harness connector between the torque sensor and EPS ECU and found the plug not fully locked.
Repair: Removed the steering column and reinstalled it with the steering wheel in the dead-centre position. Fully seated the torque sensor wiring harness connector and confirmed the locking clip engaged. Used the dedicated BYD diagnostic tool to carry out 'steering angle sensor calibration' and 'torque sensor zero-point calibration'. Performed a four-wheel alignment to ensure toe values are within specification. Road tested the vehicle and confirmed good steering wheel self-centring and no pulling to either side.
Original source ↗BYD F3 wheel speed sensor fault causing abnormal steering
Symptoms: ABS and EPS warning lights illuminated simultaneously while driving, with intermittent loss of power steering assistance and erratic speedometer readings.
Diagnosis: Retrieved DTCs indicating left front wheel speed sensor signal fault (C0032) and EPS communication error. Measured left front wheel speed sensor resistance at 1750Ω (specification 1780±150Ω); reading within acceptable range. Inspected sensor connector and wiring harness and found no visible damage. Lifted vehicle and examined driveshaft wheel speed sensor tone ring; found two missing or deformed teeth.
Fault analysis: Abnormal wheel speed signal caused ABS/ESP system to misinterpret vehicle status, affecting EPS assistance characteristic curve.
Resolution: Replaced left front driveshaft assembly (includes wheel speed sensor tone ring). Cleared DTCs from ABS and EPS systems. Performed sensor signal waveform test to confirm normal wheel speed signal. Road test confirmed ABS and EPS functionality returned to normal.
Original source ↗BYD Song MAX stalls while driving with EPS fault
Symptoms: Intermittent stalling while driving; restarts normally. EPS warning light illuminates when the fault occurs, and the steering wheel suddenly becomes heavy.
Diagnosis: Customer recorded a video of the fault, which showed multiple warning lights on the instrument cluster before stalling. Scanned the vehicle with VDS and found a communication fault between engine ECU and TCU, plus a low voltage history code in the EPS control unit. Inspected the engine compartment fuse box and found the F4/9 fuse (EPS power supply) socket had enlarged, causing poor contact. Measured EPS supply voltage during the fault; it dropped sharply from 12V to below 6V, causing the control unit to restart. Traced the wiring harness and found pins 14 and 15 of connector G09 had backed out, causing a loose connection in the power supply circuit.
Solution: Replaced the F4/9 fuse and fuse holder, ensuring tight contact. Repaired the backed-out pins at the G09 wiring harness connector and re-crimped the terminals. Inspected the VCU and rear compartment power distribution box circuits. Extended road testing confirmed the fault was completely resolved.
Original source ↗Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.