Toyota Repair: Check Engine Light on 96 corolla and clicking., front wheel bearings, emission control system

Question
Check engine light has been on for a few days on my wife's car.  I checked the oil which was dry so I filled that.  Also changed the air filter which was kind of dirty.  The light is still on and I am not sure what it may be.  I figure it is probably overdue for spark plugs also and we recently had the starter replace on it.  Any ideas what it may be.

Also, when driving the car their appears to be clicking type sound coming from the front driver side wheel.  WE got new tires put on just over a month or so ago, but I doubt it is related to that.  Could it be a bearing or something else?   I do know that I need pads and rotors on it which will be done in the next week or so.  Thanks for your help.  

Answer
Most of the time the check engine light comes on because of an emission control system failure, to find out where the problem is a scantool needs to be hooked up to the  car's diagnostic connector, this will give a trouble code as to what part of the system has a problem, most repair shops can retreive the code, if there is an Autozone store nearby you can go there, I think they will let you borrow their scanner at no charge.
The clicking noise may be coming from the brakes so have them done and see if the noise goes away, while they are doing the brakes have them check to see if any of the front wheel bearings feel loose, this could also cause a noise.