How does a fault code arise in the Network and CAN Bus group?
In a modern vehicle dozens of control units broadcast data continuously over CAN, LIN or similar buses. Codes starting with U report an interruption of that traffic: one module did not receive a message it expected from another.
The diagnostic meaning is this: a “no communication with module X” code usually does not mean module X is faulty. Far more common causes are a loss of supply or ground at that module, a break or short on the bus, a lost termination resistor, or low battery voltage. A module that stays awake when it should sleep can produce similar codes.
The order is clear: supply, ground and voltage first; then bus integrity; the module last. And communication codes arriving from many modules at once almost always point to a single common cause — chasing them one by one is wasted time.
Fault codes in this group
The database holds 27 codes in this group. Each code has its own page with the meaning, possible causes and diagnostic steps:
Read fault codes on your own vehicle
With an ELM327-based BLE OBD2 adapter, CarCoding reads confirmed, pending and permanent fault codes separately, pulls the freeze frame and explains every code in plain language. Clearing codes is done from the app as well. The app is free to download.
Some advanced features require an in-app purchase.
Data source: the CarCoding fault code database. Code definitions follow the SAE J2012 standard; manufacturers may use different wording for their own codes. Everything on this page is generated from the code-specific database records.