When I look at the LG dryer manual on this forum, it gives you several ways to test the dryer, including a diagnostic test for each component. Rather than us trying to guess what could be wrong, you could be exploring this all yourself, with your trusty meter, of course.
The fact that you see the 'cooling" displayed means it is not heating but going thru a cool-down procedure. This could be a bad sensor or a bad control, but the manual tells you how to determine which.