Trouble code · Network · Generic (all makes)

U0100 Lost Communication With ECM/PCM 'A'

Another computer in the car (often the transmission or ABS module) can't talk to the engine computer over the car's network.

Safe to drive?
Get it checked now
Limit driving until it's diagnosed
Scanner you need
Multi-system scanner
A basic reader isn’t enough
NHTSA complaints quoting it
70
Vehicle complaints, 2015–2025

Common causes

  • Weak battery or poor ground connections
  • Damaged network wiring or connectors
  • Blown fuse to the engine computer
  • Failed engine computer

Symptoms

  • No-start, stalling, many warning lights at once, gauges acting up

Can I drive with it?

Avoid driving until it's diagnosed – the engine computer losing contact can cause stalling or a no-start.

Tip: Start with the simple things: test the battery and clean the battery terminals and engine grounds.

Which scanner reads it?

Many basic code readers only show P codes. Reading U codes – and seeing which module stored this one – needs a multi-system scanner.

See ABS, Airbag and Transmission Codes for which tools read each system. Not sure which fits you? Try the Find My Scanner quiz.

In the data

Of the vehicle complaints owners filed with NHTSA from 2015 to 2025, 70 quote U0100 – most often from Chevrolet, Ford, Dodge owners. Complaints lean toward serious problems, so treat this as a sign of how often the code turns up in real reports, not how often cars get it.

Both sources are compared on the Trends page.

General information to help you understand a code – not a diagnosis. Your car’s service information or a qualified mechanic has the final word. See how we research.