What is the difference between a Electronic control module and Engine control module?

I recently bought a cheap Ford Focus which was affected in floods… I got the water of the engine and pretty much all the places, all my lights and few other electronic functions work… But my engine doesn't turn on and my HUD is dead, but works on another car… What should i do?

Those names are too vague to be exact.

JUNK ITS, ITS NOTHING BUT PROBLEMS WITH FLOOD CARS I BOUGHT A RANGE ROVER 2013, FLOOD CAR, SPENT OVER $8000.TRYING TO REPAIR IT, WE NEVER GOT IT TO START, SOLD IT FOR PARTS, TOOK A $6000. LOSS NEVER AGAIN

I don't know what an HUD is. Is it for birth control? Housing development?

Its never going to be 'fixed'. That's why the title had to denote 'flood'.

Take it to the dealer. They have the factory scan tool that can diagnose if you have communication problems in the electrical system. ECU, ECM, are pretty much the same thing. If your vehicle is an automatic it's called a PCM.

An electronic control module could be for anything. Engine control module usually just runs the engine. Now days cars often have a body control module and a power train control module. Powertrain runs things like engine, transmission, traction control, and ABS brakes. Body control module runs pretty much every other electric thing in the car.

Modern cars that were in floods are bad news. You could have just a little water in one plug somewhere in the car that will keep it from ever working correctly. Or worse yet you get it working now then next week you hit a bump and that one connector goes bad again. Only way to be sure its going to be reliable is to replace every electrical part and wire.