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Network Codes (U Codes)

Network codes report communication problems between the car's control modules on the CAN bus (controller area network). Modern cars have dozens of modules — engine, transmission, ABS, airbag, body, cluster — and they share data constantly. When one module stops hearing from another, a U code is stored.

U codes are often symptoms rather than root causes: low battery voltage, a corroded ground, water in a connector, or one failing module dragging the network down can set communication codes in several modules at once. The first checks are always the battery, grounds, and connectors — not module replacement.

There are 1,230 generic U codes in the database. Browse the complete list on the codes list page.

System clusters

Network codes with full guides