are the ignition control unit (ICU) and electornic control unit (ECU) two different devices? are they both located under the glove box?

im having ignition problems and i have seen that when the car won't start, im getting 0-4V on terminal 5 on the connector into the power stage. bentley says 0-2V. when the car eventually starts and i make the same test, its reading as it should, 0-2V. since the ICU is throwing no faults, im thinking maybe its the ICU. assuming that this signal is coming from the ICU. however, i was told by a mechanic this signal comes from the ECU?

these are 2 different parts right? i checked the wiring diagrams in bentley and they certainly appear to be different? who's the idiot here? me or my mechanic?

thanks!