"OK Google" while running android auto

So I installed the 4100nex and mapped the audio controls to my 2005 Altima SE-R steering wheel controls but It doesn't have a microphone button. So every time I want to search for something I have to touch the mic button on the head unit while using android auto. I DON'T want to have to do this and was wondering why OK Google won't work even after setting my M8 to always listen for the commands? Does android auto app automatically turn off that function when connected to the HU? I am sure other folks with cars without microphone buttons and android auto head units have similar issues?

Thanks!

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