4XX Errors
4xx errors (also referred to as 400 errors) occur when a page that once existed on a website is no longer live and has not been redirected elsewhere. These HTTP 4xx status codes (such as a 404 error) can also impact SEO. There are a number of ways search engines view and deal with pages displaying 4xx error codes.
Learn how Google Search views 400 errors on your website (and how to solve 4xx issues for better organic search results) in this collection of ‘SEO Office Hours’ notes.
For more on 4xx errors, see our article on how to find 404 errors on your site.
Further reading: The ABCs of HTTP Status Codes
301/404 Won’t Cause Ranking Problems
Large numbers of 301 redirects and expired/low value URLs which 404 won’t directly cause any general ranking problems for the site (assuming you’re doing them properly and not losing important pages). But try to avoid chains of mutliple redirects.
Soft 404 Errors Can Identify Thin Pages
The Soft 404 errors report in Webmaster Tools is a good way of identifying thin pages which Google don’t think have any original content.