U0100: Lost communication with engine control module

What does it mean?

System

Network (communication between control units)

Type of code

Generic code: means the same on every make.

How urgent?

Do not drive further than you need to: carrying on can damage the engine, the catalyst or other parts. If the engine light is flashing, stop safely as soon as you can.

Possible causes

• Weak battery or an alternator not charging well
• Poor ground connection or damaged wiring
• Corrosion or moisture in a connector
• Control unit or software

Tip: don’t just clear the code. Clearing a code doesn’t fix the cause. It often comes back, and the stored data that helps us find the cause is then gone.