What does U0100 mean?

Other modules can no longer communicate with the engine control module.

Can a blown fuse cause U0100?

Yes. A power or ground problem at the ECM is a common cause.

Network communication

U0100 — Lost Communication With ECM/PCM A

Another control module cannot communicate with the engine control module (ECM/PCM). Without the ECM many systems stop working properly and the engine may not run.

Severity: High

Common causes

Faulty ECM/PCM or its power and ground supply
CAN bus wiring fault (open, short, corroded connector)
Blown ECM fuse or relay
Low battery voltage
Another module disturbing the CAN bus

Symptoms

Engine does not start or stalls
Multiple warning lights
Gauges or transmission behave erratically
Several U codes in other modules

How to check

Check battery voltage and the ECM fuses, relays and ground
Check CAN wiring and connectors to the ECM
Scan all modules to see which ones lost the ECM
Check ECM power supply pins and test the module if everything else is good

Can you keep driving?

Not recommended: the engine may stall or not start. Diagnose the cause before driving.

Frequently asked questions

What does U0100 mean?: Other modules can no longer communicate with the engine control module.
Can a blown fuse cause U0100?: Yes. A power or ground problem at the ECM is a common cause.

General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.