EOS 1n will not Autofocus

SOURCE: Canon EOS Rebel T2 300X Won't Autofocus or Take Picture

This may be a problem with the autofocus itself, try the following:

• If you have a different lens, see if the autofocus works with the other lens. If it does, there may be something wrong with your lens.
  
• Clean the contacts (the little metal things between the lens and the camera) with a slightly moist, lint-free cloth
• Try replacing the battery in the camera

SOURCE: autofcous and manual focus do not work

excuse me if this is a dumb question but you wouldn't believe the things people do...., but in manual mode are you actually manually trying to move the lens? as manual mode means just that you take hold of the lens and turn it. If it wont turn it sounds like the lens is jammed and needs returning/repairing.

if taking hold of the lens and turning it works for manual mode, take the lens off and clean the gold contacts on both the camera and the lens with a pencil erasor this may bring the auto focus back to life, switch back to auto and try again, if not its most likely the lens but take the body to a canon store and try another lens just to double check the body is ok

drop me a line if i can be of further assistance

best of luck

SOURCE: canon eos rebel II

Try removing the camera lens and VERY CAREFULLY raise the mirror in the camera. There is another small mirror behind the main mirror that relects the light for the autofocus to work. If the spring on that small mirror is broken (common problem) it can cause the symptom you are experiencing.

You can also check it by aiming the camera at an object above your head with the camera pointed up since that will hold the little mirror in place by gravity. If it works pointed up the spring is the problem.

You can get the spring from Canon. The part number is CS2-6367-000. Canon's parts dept phone number is 1-732-521-7230.

CameraRepairs

SOURCE: Canon Rbl XT out of focus in viewfndr when shutter half way down

Hello,
It's possible that the reason the "pictures turn out fairly good" is that your f-stop is set high enough that even though the image isn't properly focused, you have enough depth-of-field to bring your subject into "near focus". Does your lens try to focus back and forth when you half-press the shutter? If not, double check that the lens is in autofocus and not manual focus. You can also try cleaning the contacts between the lens and camera. Take the lens off, and then one-at-a-time clean the contacts on both the lens and the camera, using a clean pencil eraser. Gently rub the contacts. Be sure to hold the item upside down so that the eraser debris falls on to the table, not into the camera body or lens!

If none of this helps the autofocus may have become damaged and you need to have the lens and camera looked at by Canon Repair.

SOURCE: autofocus function will not work on Canon 17 40mm 1.4 EF lens

Since the problem is limited to this lens, I highly doubt that you would have to replace the cameras AF sensors.
Since you only have the problem with this lens, I am afraid that you will have to get the lens repaired. Is the lens also 3 years old? Did you get it with MACK extended warranty?
Sometimes, Canon do these kinds of repairs for free, if they discover that there was some manufacturing error that caused it to fail. So be sure that you get it to a certified canon workshop. 
I hope this helps, 
/Chris