Autofocus on lens that came with Canon EOS 450D not working

[MTA-P]

My wife bought a Canon EOS450D second hand, and the autofocus just isn't working. It works fine in manual focus mode, but in autofocus mode, it doesn't focus, and nothing happens when you click the shutter. 

I thought I'd fixed it because when I put it in manual focus mode, and put the object out of focus, then out in back into autofocus mode, it worked. But it only worked under these circumstances. If it has to change focus from one object to another, it doesn't do it. 

It works perfectly with other lenses we own, so we know the issue is the lens, not the camera body. But from searching on the web, it seems that issues with lenses usually involve physical damage, which can be diagnosed if the lens makes a whirring noise as it tries to focus, or you hear clicking or crunching sound as you turn the focus ring. Neither of these is happening. The lens seems physically fine. It's as if the lens is simply not communicating with the camera body. I've tried cleaning the contact points with isopropyl alcohol, but that didn't help. 

[Tronhard]

Hi and welcome to the forum:
First, it would be really, really helpful to know what lens you are talking about?  The fact that it came with the EOS 450D somewhat suggests that it is an old model, but without a specific description (so, for example, simply saying 18-55 is not precise enough) as there are often multiple versions of lenses of a focal range with different characteristics.

[MTA-P]

Thank you so much for your response. 

It is an 18-55mm lens...

The front says "Canon Zoom Lens EF-S 18-55mm" 1:3.5-5.6 IS"

I hope that tells you what kind it is, because we're both laypeople, and I can't say much more about it. 

The seller insists that it's the lens that came with the original body though, if that helps. 

[Tronhard]

Thank you for that response.

As my colleague said, there is a possibility that the lens is worn out, as that is a very old model.  However, there is a possibility that the operation has been inadvertently compromised by one of you.
With these older models, one cannon attempt to manually focus the lens while the AF-MF switch on the lens is set to ON (or AF), doing so will cause the lens focusing mechanism to get out of alignment and cause it not to focus properly.

There is a possible fix for this:
1.  Take the lens off of your camera.
2. Put the lens in MF mode.
3. Twist the FOCUS ring (the tip of the lens) all the way to one side (extend it). You may hear a click noise or two, this is good, but don't FORCE the lens.
4. Twist the FOCUS ring all the way to the opposite side (retract it). Again, you may hear a couple of clicking noises. What we hope is happening is the focusing motor being put back into its proper place.
5. Put the lens back on the camera.
6. Put the lens in AF mode.
7. Turn the camera on.
8. Put the camera in AUTO or P mode.
9. Take a test photo.
If that does not work, then it is fairly likely that the lens has suffered a malfunction and it will not be viable to have replaced - a replacement optic is much better technology.  If you wish to replace the lens you would be best to consider one of the following two:
EF-S 18-55 IS STM lens exactly replicates the range you have, but is much faster, smoother focus and can be focused manually with AF active.
EF-S 18-135 IS USM, will over a much wider focal range, also fast and silent focus and can be focused manually with AF on.   This is a superior optic.
You could look for a good second-hand unit at KEH.COM (Canon do not appear to be selling refurb EF-S lenses on their site).

[normadel]

It sounds like your lens has just given up the ghost. If you like the zoom range, replace it with one of the two latest versions.

There have been nine versions of the EF-S 18-55 "kit" lens. The two latest are f/3.5-5.6 IS STM and f/4-5.6 IS STM. You can find excellent used ones online. I have three of them, bought from MPB.com for $55-65 each. The current f4-5.6 is $249.00 new, Both STM versions provide Full-Time Manual Focus (you can manual-focus without switching the lens of AF mode). Also, they are internal-focus, so the front of the lens does not rotate, which is good if using polarizers. Smooth, fast, quiet focusing. Very nice little lenses.