Radio does not go below 90FM

[scirocco]

In a 2001 BMW X5 3.0 I bought, there was an aftermarket iSimple Aux input in the ashtray area. The little unit has a switch and an Aux input. Reading up on it, it seems that this will work at 88.7Fm.

But when I try tuning the MID to 88.7, it never wants to tune below 90.1FM. What do I need to do to make it tune below 90.1. I tried the manual tuning by pressing the m button and then the left arrow.