U0100

Lost Communication With ECM/PCM

Severity: High Network / Communication Generic OBD-II Code Est. Repair: $100 - $1,500+

High severity. Avoid long drives and get diagnosed as soon as possible. Flashing check engine light = stop driving if safe.

What Does U0100 Mean?

A module lost communication with the ECM on the CAN bus.

Common Symptoms

Multiple warning lights
Possible no-start or limp
Communication errors

Possible Causes

CAN wiring open/short
Failed ECM
Power/ground to ECM
Software
Aftermarket device interference

How to Fix U0100 – Repair Guide

Check ECM power and grounds
Inspect CAN H/L
Scan all modules for U-codes
Check aftermarket electronics
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Disclaimer: Information is for educational reference only and does not replace professional diagnosis. Actual causes and costs vary by vehicle make, model, year and condition. Always verify with a qualified technician.