What are the common causes of U0051?

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

Read the code and check module communication status on a scan tool. Test the Bus C negative wire for continuity end to end. Check the Bus C negative connector pins for corrosion or backing out. Measure bus resistance across the Bus C terminals. Repair the open in the Bus C negative circuit. Clear the code and retest.

U0051

Vehicle Communication Bus C (-) Open

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

What it means

U0051 means Vehicle Communication Bus C (-) Open.

Check these first

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

What to do next

Read the code and check module communication status on a scan tool
Test the Bus C negative wire for continuity end to end
Check the Bus C negative connector pins for corrosion or backing out
Measure bus resistance across the Bus C terminals
Repair the open in the Bus C negative circuit
Clear the code and retest

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Updated

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