AU
U0146

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

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 — Seal U
  • 1Gateway Controller (GWC) power supply or ground circuit fault, causing intermittent or permanent power loss to the gateway.
  • 2Physical damage to the CAN bus wiring (chafing, crushing, water ingress) causing a short circuit, open circuit, or excessive contact resistance in CAN-H and CAN-L.
  • 3Gateway controller internal hardware fault or outdated software causing a communication protocol mismatch.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 systems 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 to 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) at the gateway controller (usually located under the dashboard or center tunnel). Voltage must measure 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 OBD diagnostic connector. Normal values are 2.5V-2.7V and 2.3V-2.5V respectively. Measure the terminating resistance; it must 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. Check connectors for water ingress, oxidation, or looseness.
  • 5
    Disconnect the 12V battery negative terminal. Measure the CAN termination resistance of the SRS and gateway separately (if equipped). Check for open or short circuits.
  • 6
    Check gateway and SRS software versions. If a Technical Service Bulletin (TSB) recommends an upgrade, update the software.
  • 7
    If the wiring is normal, test by substitution: first replace the gateway controller and test. If the fault persists, replace the SRS control unit (synchronize the immobilizer and airbag coding).
  • 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 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.