Setting 404_override

Hi everyone, 

This is the first day I've ever played with codeigniter for more than 10 minutes, and this is the first time I've built something from scratch. 

I'm setting the 404_override variable in the /application/config/routes.php file. I want to set it to 'errorh/pages/404' so it would call the 'Errorh' controller, the 'pages' function and set the first variable to '404'. 

Except everytime I do this, it tries to tell me that a function called pages/404 is missing? Am I being stupid here? It works on the rest of the routes I've setup, but not on the 404_override one.

Is it possible that this specific route cannot support passing a variable over like the other ones do? 

Thanks in advance everyone!