What are the common causes of U0013?

A short to ground on the medium speed CAN positive wire. A partially shorted medium speed CAN positive connector. A module pulling the medium speed CAN positive voltage low. Water intrusion in the medium speed CAN positive harness.

Read the code and check module communication status on a scan tool. Measure medium speed CAN positive voltage with the key on. Test the medium speed CAN positive wire for a short to ground. Inspect the medium speed CAN positive connectors for moisture. Disconnect modules one at a time to find the one pulling the line low. Clear the code and retest.

U0013

Medium Speed CAN Communication Bus (+) Low

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

What it means

U0013 means Medium Speed CAN Communication Bus (+) Low.

Check these first

A short to ground on the medium speed CAN positive wire
A partially shorted medium speed CAN positive connector
A module pulling the medium speed CAN positive voltage low
Water intrusion in the medium speed CAN positive harness

What to do next

Read the code and check module communication status on a scan tool
Measure medium speed CAN positive voltage with the key on
Test the medium speed CAN positive wire for a short to ground
Inspect the medium speed CAN positive connectors for moisture
Disconnect modules one at a time to find the one pulling the line low
Clear the code and retest

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Updated

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