It normally inside the fender for the fronts and under the trunk panel or inside the fender for the rears on the receiver.
But also there's a receiver and module, so it's a two parts that you need to look for and see which one is bad. Also check your fuses, there's some behind glovebox as well in the trunk and also under the hood.
I'm not a mechanic, this is what I learned from my Errors in past. Hope it helps, please post is you find it and what's the outcome..
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