AU
U0146

DTC U0146 indicates a loss of communication between the airbag control unit (SRS ECU) and the vehicle gateway controller (Gateway Control Module) — Atto 3

Safety System

DTC U0146 indicates a loss of communication between the airbag control unit (SRS ECU) and the vehicle gateway controller (Gateway Control Module).

The gateway acts as the data exchange hub between different vehicle CAN bus networks (such as powertrain CAN, comfort CAN, and chassis CAN) and routes information between control units.

When the SRS system cannot communicate with the gateway, the airbag system becomes isolated.

It cannot receive critical signals from other systems (such as crash signals, vehicle speed signals, and high-voltage interlock status).

Additionally, during a collision, it cannot send commands through the gateway to other systems (such as cutting off the high-voltage power supply, unlocking the doors, and turning on the hazard lights).

This may degrade or disable crash protection functions, creating a serious safety hazard.

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Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Gateway Controller (GWC) power supply or ground circuit fault causing intermittent or permanent gateway power loss.
  • 2Physical damage to the CAN bus wiring (wear, crushing, water ingress) causing a short circuit between CAN-H and CAN-L, an open circuit, or excessive contact resistance.
  • 3Gateway controller internal hardware fault or outdated software causing a communication protocol mismatch.
  • 4Airbag Control Unit (SRS) internal communication module fault or poor connector contact
  • 5Unauthorized vehicle modifications (such as aftermarket navigation units or dash cams) connected to the CAN network, causing signal interference or excessive bus load.
What To Do
  • 1
    Use the VDS2000/VDS1000 diagnostic tool to perform a full vehicle scan, record the communication status and fault codes of all modules, and confirm whether it is a single-module or multi-module communication fault.
  • 2
    Check the power supply (constant power BATT, ignition power IG1) and ground (GND) of the gateway controller (usually located under the dashboard or center console tunnel). Measure the voltage and resistance: voltage must be within 12V±0.5V, and ground resistance must be less than 1Ω.
  • 3
    Measure the voltage at pins 6 (CAN-H) and 14 (CAN-L) of the diagnostic connector (OBD). Normal voltages are 2.5V-2.7V and 2.3V-2.5V respectively. Measure the terminal resistance; it should be approximately 60Ω (two 120Ω resistors in parallel).
  • 4
    Inspect the CAN wiring harness between the SRS control unit and the gateway, focusing on wear-prone areas such as the firewall, A-pillar, and floor harness routing holes. Inspect the connectors for water ingress, oxidation, or looseness.
  • 5
    Disconnect the battery negative terminal. Measure the CAN termination resistance of the SRS and gateway separately (if equipped) and check for an open or short circuit.
  • 6
    Check the gateway and SRS software versions. If a Technical Service Bulletin (TSB) recommends an upgrade, perform a software update.
  • 7
    If the wiring is normal, perform a substitution test: first, replace the gateway controller. If the fault persists, replace the SRS control unit (match the immobilizer and airbag coding simultaneously).
  • 8
    After repair, clear the fault code, perform a road test, and rescan to confirm communication is restored and the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

BYD Song - Multi-system network fault (including communication faults similar to U0146)

✓
Symptoms: While driving, the dashboard suddenly displayed multiple warnings: "Check Engine System", "ABS System", "Network", and "Brake System". Vehicle performance restricted. Diagnosis: Scanned with VDS1000. Found ECM stored communication fault codes related to the Body Control Module. Checked CAN network voltage and termination resistance; resistance was below standard (60Ω). Inspected the CAN harness section by section and found wiring below the right A-pillar worn through, shorting CAN-H and CAN-L. Resolution: Repaired the damaged CAN harness below the right A-pillar, re-wrapped and insulated the wiring, cleared fault codes, and road-tested. All system communications returned to normal.
Original source ↗
BYD DTC AI Analysis

BYD Qin 80 - CAN network failure causing no-start condition (U0146-type fault)

✓
Symptoms: Intermittent flashing P gear indicator, no SOC display. Instrument cluster showed multiple system warnings including "Check ESP System" and "Check EPB System." Vehicle would not enter Ready mode. Diagnosis: Vehicle was normal on arrival, confirming intermittent fault. No modifications or aftermarket accessories found. VDS scan showed multiple modules reporting communication errors, including abnormal communication with the left body domain controller. Measured CAN voltage at diagnostic port: CAN-H 2.3V, CAN-L 2.7V (normal ~2.5V). Sectional testing found water ingress in the left front door wiring harness connector causing abnormal CAN signals. Resolution: Cleaned water from left front door wiring harness connector, applied conductive grease, and resecured waterproof seal. Fault cleared.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM - All dashboard warning lights intermittently illuminate (network communication fault)

✓
Symptoms: While driving, all instrument warning lights intermittently illuminated, the speedometer went blank, and power steering assist dropped out. Restarting did not help; the system sometimes recovered after sitting idle. Diagnosis: Scanned with VDS and found multiple modules simultaneously reporting communication faults. Checked pin 16 (power) and pins 4/5 (ground) at the OBD port — supply checked normal. Measured the CAN waveform and found abnormal noise. Disconnected modules one by one; disconnecting the smart entry controller cleared the fault. Power and ground at the smart entry controller checked normal. Replaced the controller and verified the CAN waveform returned to normal. Resolution: Replaced the smart entry controller, rematched the immobiliser, and eliminated the fault.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro - Dashboard displaying 'Key Not Detected' (network communication fault)

✓
Symptoms: Rotating PAD screen stayed on constantly. Attempted to restart vehicle but failed. Instrument panel displayed "Key Not Detected." Remote key unresponsive. Diagnosis: No modifications or aftermarket accessories found. VDS scan showed multiple modules offline, including intermittent BCM (Body Control Module) communication. Measured BCM supply voltages: constant 12V normal; IG1 dropped to 9.5V. Checked IG1 power circuit between instrument panel fuse box and BCM; found poor contact at intermediate connector. Wiggling the wiring harness caused BCM communication to drop in and out. Fix: Cleaned and tightened IG1 power connector between instrument panel fuse box and BCM, replaced corroded terminals. Fault cleared.
Original source ↗
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.