OBD Codes List

Diagnostic reference · U0030

U0030

Vehicle Communication Bus A (+) Open

System
Network communication (U code)
Lamp
Check Engine Light
Category
Network Communications

What it means

U0030 means Vehicle Communication Bus A (+) Open.

Check these first

  • An open in the Bus A positive wire
  • A broken or corroded Bus A positive connector pin
  • A module that has lost its Bus A positive connection
  • Harness damage that cut the Bus A positive conductor

What to do next

  1. Read the code and check module communication status on a scan tool
  2. Test the Bus A positive wire for continuity end to end
  3. Check the Bus A positive connector pins for corrosion or backing out
  4. Measure bus resistance across the Bus A terminals
  5. Repair the open in the Bus A positive circuit
  6. Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.