What are the common causes of U0020?

Intermittent opens or shorts on the low speed CAN. A failing transceiver on one module on the low speed CAN. Corroded or water damaged low speed CAN connectors. Electrical noise on the low speed CAN.

Read the code and check module communication status on a scan tool. Monitor low speed CAN traffic for dropped or error frames. Inspect the low speed CAN connectors for corrosion or moisture. Check for aftermarket devices that may add noise. Replace the module that shows intermittent communication loss. Clear the code and retest.

U0020

Low Speed CAN Communication Bus Performance

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

What it means

U0020 means Low Speed CAN Communication Bus Performance.

Check these first

Intermittent opens or shorts on the low speed CAN
A failing transceiver on one module on the low speed CAN
Corroded or water damaged low speed CAN connectors
Electrical noise on the low speed CAN

What to do next

Read the code and check module communication status on a scan tool
Monitor low speed CAN traffic for dropped or error frames
Inspect the low speed CAN connectors for corrosion or moisture
Check for aftermarket devices that may add noise
Replace the module that shows intermittent communication loss
Clear the code and retest

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Updated

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