What is the white cube beside the ECU?

Hello, looking at the schematic, I don't see any other component next to the engine powertrain control module. I'd suggest getting the guidance of a local shop near you who can weigh in on identifying the component in question. https://repairpal.com/auto-repair-near-me

Hi! this is Bo with Car Genius at RepairPal! Is there an aftermarket alarm or stereo installed? I'd really have to see a picture of it to verify what it could possibly be. Feel free to call the number below and I'd be happy to help you figure it out! If you have any other questions feel free to give us a call at 877-913-1554! We'll be happy to help or find you a certified shop in your area!