Network Communication OBD2 Codes (U-Codes)
Network Communication diagnostic trouble codes begin with the letter U and identify faults involving communication between electronic control modules. Browse our database of 5 published U-codes covering CAN bus, module communication and other vehicle-network faults.
What Are Network Communication OBD2 Codes?
Modern vehicles contain multiple electronic control modules that exchange information through communication networks such as CAN bus. U-codes are stored when a control module detects missing, invalid or unexpected communication with another module or network.
A Network Communication code does not automatically mean that the module named in the fault is defective. Low battery voltage, wiring faults, damaged connectors, network shorts, poor grounds or another failed module can also interrupt communication.
How to Read a U-Code
A Network Communication trouble code begins with the letter U followed by four characters. The code identifies the communication or network fault detected by one or more vehicle control modules.
Common Causes of Network Communication Codes
- CAN bus wiring faults
- Open or shorted communication circuits
- Damaged wiring harnesses or connectors
- Low battery or charging-system voltage
- Missing power supply or ground to a control module
- Faulty electronic control modules
- Incorrect module configuration or programming
- Communication faults between ABS, ECU, TCM, BCM and other modules
Browse Network Codes by Family
Standardized communication trouble codes covering CAN bus, control-module communication and vehicle-network faults.
Network communication definitions in this range may depend on the vehicle manufacturer, model and electronic architecture.
Additional communication and vehicle-network diagnostic definitions used by electronic control systems.
Further vehicle-network trouble codes whose exact definition may depend on manufacturer and control-module configuration.
Browse Network Communication Trouble Codes
Showing Network Communication OBD2 codes from our database of 5 published U-codes.
Generic vs Manufacturer-Specific Network Codes
Some U-codes use standardized definitions while others are defined by the vehicle manufacturer. For manufacturer-specific communication faults, confirm the exact vehicle, control modules and network architecture before diagnosing the fault.
How to Diagnose a Network Communication DTC
Start by scanning all available vehicle modules rather than only the engine ECU. Identify which modules respond normally and which modules cannot be reached.
Check battery voltage, module power supplies and grounds before investigating the communication network. Inspect CAN wiring and connectors for opens, shorts, corrosion or physical damage.
When several modules report loss of communication with the same control unit, the shared network path, power supply and the affected module should be checked before parts are replaced.
Network Communication OBD2 Codes FAQ
What does U mean in an OBD2 code?
The letter U identifies a diagnostic trouble code associated with communication between vehicle electronic control modules and networks.
Does a U-code mean the CAN bus is faulty?
Not necessarily. CAN wiring can cause a U-code, but module power, grounds, connectors, battery voltage and individual control modules can also interrupt communication.
Can a basic OBD2 scanner read Network codes?
Capabilities vary by scanner and vehicle. A basic engine-code reader may not access every vehicle module, while an advanced diagnostic tool can communicate with multiple control systems and retrieve additional U-codes.
