// Official meaning
Lost communication with the ECM/PCM — other modules can no longer reach the engine ECU on the vehicle network.
// On the bench
The tell-tale pattern: the engine ECU is silent on the diagnostic port while every other module answers fine. Before condemning anything we check power feeds, grounds and the network — but when the feeds are good and the unit stays mute, the ECU itself has failed. Cranks-but-no-start with no communication is one of the most common ways a dead ECU presents.
How it shows up
- Engine cranks but will not start
- No communication with the engine ECU; other modules respond
- Multiple warning lights across the dash
- Often follows a jump start, battery change or water ingress
What fixing it involves
Proper diagnosis first — power, grounds, network — then component-level repair of the original ECU from £150 (typical £190). If the unit is beyond economic repair we clone your data onto a donor so the car still starts on your existing keys.
Frequently asked questions
Could U0100 just be a blown fuse or broken wire?
It can be, which is why power and ground checks come first — no honest diagnosis skips them. But when the feeds test good and the module stays silent, it is the ECU, and that is the majority of cases we see.
My car died after a jump start and now shows U0100 — related?
Very likely. Jump-start mistakes and overvoltage kill ECU power stages — it is one of the classic ways these units die. Send us the part number and symptoms and we will give you a straight answer.