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
404 Content Isn’t Seen by Google
Google doesn’t look at the content of a 404 page
Status Codes and Disavows are Not Permanent
404 and 410 do not have permanent effects. If you change them back to 200 then the pages will become indexed again, or redirects will start to pass PageRank. Disavow also isn’t permanent, so if you remove the URLs from the disavow file they will start to pass PageRank, although this won’t happen until the URLs are recrawled.
s Are Recrawled Periodically
Google will remember your 404 URLs for a long time, and periodically recrawl them to see if they are still 404. These will be reported in search console, but are perfectly fine.
PageRank to 404 Pages is Lost
Any PageRank acquired for pages which return a 404 is lost.
Many to One 302 Redirects Will Be Treated as 404
URLs which are 302 to the home page on any large scale will probably be treated like a 404 and dropped from the index, and pagerank won’t be passed.
Google Ignores Content on 404 Pages But Recrawls Them
Google ignores all content on pages which return a 404 status, but will continue to crawl them periodically.
Redirecting to 404 is OK
A 302 redirect to a 404 page is OK
PageRank to 404 Pages is Lost
If a site links to an external page which returns a 404, the PageRank will be lost.
404 Pages Crawled Less Than Noindex
For expired/removed content, John says that Google prefer a 404 as it results in less crawling than a noindex.
Redirect Expired Pages to Alternatives or 404
Out of stock/expired pages can be managed in a variety of ways. If there is a relevant alternative product, or a category page with good alternatives, a redirect is OK, otherwise a 410/404 is best.