Lost communication with ECM/PCM
What U0100 means
Your car's computer set U0100: Lost communication with ECM/PCM. It belongs to the network communication group of codes. It is a generic code, so it means the same thing on every make. The check engine light usually comes on once the fault has been seen on two drives in a row. Until then it shows up as a pending code.
Can I keep driving? Depends on which module dropped out. If warning lights for ABS, airbags or the gauge cluster are on, get it checked soon.
Common causes
- Low battery voltage
- Loose connector or damaged wiring on the network
- The module that stopped talking has failed or lost power
- Water in a connector
Fix the cheapest, most likely cause first. Clearing the code without a repair only turns the light off until the fault comes back.
Check it yourself
Run the Battery & charging test in Mods first. Network codes often follow a weak battery or a jump start.
Torque Deck reads U0100 with a cheap Bluetooth OBD2 adapter. It also shows the freeze frame (engine conditions at the moment the code set) and the live data you need to narrow it down.
Related codes
This page explains what the code usually means. It is not a diagnosis of your car. When in doubt, ask a mechanic.