U0100 Lost Communication With ECM/PCM "A"

Network Severity: High Generic OBD-II

Another module cannot talk to the engine computer.

Common causes

  • Engine computer without power or ground
  • Network wiring problem
  • Faulty engine computer

Symptoms

  • No start
  • Several warning lights
  • Gauges dropping out

What to check

  1. Check engine computer fuses and grounds
  2. Check network wiring
  3. Scan all modules

Manufacturers may add their own detail to generic codes. If your vehicle shows a different description for U0100, follow the service information for that make and model.

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