How does Crawl Errors in Google work?

Question

Google

In Google's Webmaster, got Crawl Errors . Indicates that there are links on the page, when you click on them, you get a 503 error.
When I go to the specified page where there are these links, there are no links in the source code of these links.
Q : How does the data service work? Whether it disables scripts when scanning a page or not, and so on.
Because of what an error:
On the page there are two select'a. For example, in the first one there is a list of car brands, and the second select in the disabled status until the first one is selected.
And now Google shows that there is an audi / jazz link, but there is definitely no such link on the page.
The code inspector has a complete list of all brands and all models in the option.