Michael and KITT relationship

I'm sorry that you did not understand what KITT was.

Perhaps if you had watched more episodes you would have understood, that KITT was not a talking "Car" or "Voice Machine" as you put it...

While the acronym of K.I.T.T. stood for the Knight Industries Two Thousand... which was essentially referring to the whole car... Most of the time what Michael thought of as KITT, was the Central Processing Unit. The computer that controlled the car. The Trans Am was just KITT's body. There was a few times during the series, and in Knight Rider 2000, KITT's CPU was separated from the Trans Am. KITT was still KITT.

The CPU, was like a brain. KITT's mind and personality. Unfortunately the show was not good at clarifying what that meant, but KITT was an Artificial Lifeform. How Wilton Knight accomplished this, and how Bonnie "recreated" him in "Junk Yard Dog", is unknown...

KITT was sentient, and also experienced emotions such as fear, so he was alive, just like some of these other fictional characters...

C-3PO & R2D2 from Star Wars.
Number "Johnny" Five from Short Circuit.
Lt. Commander Data, from Star Trek.

Every one of those Characters had human friends, just like Michael was KITT's friend.

There were times where KITT was seriously damaged, and Michael was deeply worried that he may lose his friend. Just like if anyone had a human friend that gets severely injured.