Toyota Repair: ECU Repair, maximum efficiency, expertice

Question
Check engine light on. I have been told that the computer that gives instructions to my engine must be replaced.  Not an emergency; they had no problem with my driving the vehicle for the 2 weeks it will take to obtain the part.  The "explanation" is that the commands by the computer are not being given correctly, and the cylinders are not operating at maximum efficiency.  (1) what is the name of this part? (2) how much should it cost/where can I order it myself (guys at my dealership are on COMMISSION)? (3) can you give me a better explanation with the little I have given you to go on?  Thanks for your expertice.

Answer
I have NO idea what make, model, year, or miles this vehicle is !!!!

If the engine light is on that DOES NOT mean you need to replace the
ECM(computer) !!!! A sensor is telling the computer that something is
slightly off, its not a bad sensor !!!! If its the 02 sensor just drive it.
Go to a auto parts store, they will hook up a scanner for free !