What are the common causes of U0071?

A short to voltage on the bus E (-) wire. A module on bus E driving the (-) line above its normal level. A bad ground forcing the bus E (-) reference high. An added accessory backfeeding the bus E (-) line.

Read stored codes on every module that shares bus E. Measure the bus E (-) line for a short to voltage. Check the ground points shared by the modules on bus E. Disconnect added accessories one at a time to rule out a backfeed. Replace the module driving the bus E (-) line high. Clear the code and retest.

U0071

Vehicle Communication Bus E (-) High

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

What it means

U0071 means Vehicle Communication Bus E (-) High.

Check these first

A short to voltage on the bus E (-) wire
A module on bus E driving the (-) line above its normal level
A bad ground forcing the bus E (-) reference high
An added accessory backfeeding the bus E (-) line

What to do next

Read stored codes on every module that shares bus E
Measure the bus E (-) line for a short to voltage
Check the ground points shared by the modules on bus E
Disconnect added accessories one at a time to rule out a backfeed
Replace the module driving the bus E (-) line high
Clear the code and retest

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Updated

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