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U0100: Lost communication with engine computer (ECM/PCM)
Fix soonSystem: Network and modules
What U0100 means
Other modules cannot talk to the engine computer. Check the battery and grounds first, because low voltage often causes network codes.
Common symptoms
- Dashboard lights or gauges acting oddly
- Stalling
- Hard starting
Common causes
- Communication network wiring fault
- Weak battery or bad terminal connections
- Poor ground connection
- Failed control module (uncommon)
Can I keep driving?
Fix soon. Usually drivable for a short time, but get it checked soon. Ignoring it can waste fuel, raise emissions and lead to more damage.
What to do next
- Write down the code and any symptoms you notice.
- Check the simple things first: the fuel cap, loose connectors and fluid levels where they apply.
- Do not just clear the code. If the light comes back, the cause is still there and needs a proper diagnosis.
- Read live data and freeze frame data with an OBD-II scanner app to see what the car was doing when the code was set.
Read U0100 from your own car
DriveHub connects to a $15 to $30 OBD-II adapter, reads the code from your car and explains it in plain English. iPhone and Android.
General information, not a diagnosis. Causes vary by make, model and engine. If you are unsure, have the car inspected.