PHP - Create error status for ajax return

To perform a system validation I need to create an error status and get this status in ajax at:

error: (function (erro) {
    //codigo 
})

Based on http_response_code(404); of PHP .

Can I create a 603 error and get this error 603 in ajax return?

I tried to change / include the status 603 in http_response_code("603"); but in ajax return, I got the code 500