U0100: Lost Communication With ECM/PCM A
Another module lost contact with the engine computer over the vehicle network.
Green, yellow, red: three ways U0100 can look
The same code can be a quick fix or a reason to pull over. Match your situation to the closest example.
Keep an eye on it
Logged once after a battery change or jump start.
Schedule a repair
Warning lights come and go. Diagnose soon; it can become a no-start.
Stop and get help
Stalling while driving or no-start. Don't drive it.
Symptoms you might notice
- Stalling or no-start
- Several warning lights
- Gauges dropping out
Common causes, cheapest first
- Low battery or bad ground
- Blown engine computer fuse
- Damaged network wiring
- Failed engine computer
What you can check before calling
- Check battery terminals and grounds
A code points to a system, not a part. Replacing parts based on the code alone is how people spend money without fixing the problem. Testing confirms the cause first.
Generic codes (second character 0) mean the same thing on every vehicle. Some manufacturers add their own details, so check service information for your exact vehicle.
Related codes
More network & modules codes
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does U0100 mean?
U0100 means "Lost Communication With ECM/PCM A". Another module lost contact with the engine computer over the vehicle network.
Can I drive with code U0100?
It depends on what the vehicle is doing. Green: Logged once after a battery change or jump start. Yellow: Warning lights come and go. Diagnose soon; it can become a no-start. Red: Stalling while driving or no-start. Don't drive it.
What causes U0100?
The most common causes are: low battery or bad ground; blown engine computer fuse; damaged network wiring.
Is U0100 a serious code?
It can be. Stalling while driving or no-start. Don't drive it.
Skip the shop. We'll come to you.
Book online in about a minute, or call or text the office. We'll confirm the details and get a mechanic headed your way.