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Network (U)

U0100: Lost communication with ECM/PCM

This code means that a module has lost communication with the engine control module (ECM) or powertrain control module (PCM). It indicates a problem in the vehicle's communication network.

Checked by a licensed car technician · last reviewed 29 September 2026

Symptoms

  • Engine warning light on
  • Possible engine performance issues
  • Communication errors with diagnostic tools

Common causes

  1. Low battery voltage
  2. Faulty CAN wiring
  3. Power supply issue to a module
  4. Faulty ECM/PCM
  5. Faulty module

How to check it yourself

  1. Check battery voltage
  2. Inspect CAN wiring for damage
  3. Ensure power supply to modules is intact
  4. Check ECM/PCM connections
  5. Use diagnostic tool to check for other codes

Can I keep driving?

The car can usually be driven, but performance may be affected. Seek repair soon.

General guidance, not a professional inspection. Confirm faults with measurements before buying parts, and use a qualified mechanic for brakes, steering, fuel leaks, airbags, and other safety-critical work. Terms and disclaimer

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