Are phone emitting / checking on all bands?

Hi guys,

My question is simple but yet complicated I think. I have a 4g network on my phone, different carriers emits from different frequencies.

If my phone is set to use "LTE only" for example, will it keep looking for bands which are not supported by my carrier, or will it only use the bands for my carrier? Thanks in advance

I dunno if this is the right place to ask but I try my luck