Volvo Repair: Check Engine and wheel bearing., wheel bearing, hub assembly

Question
Thanks!  Any insight on the (315) check engine code?

I tackled the rear brakes last night too; interesting cars.  This is my first volvo.  I'm going to tackle the shocks and struts tonight or this weekend.  Anything special I should keep in mind there?
-------------------------

Followup To

Question -
Hello!  I've found this site very useful, including many of your posts.  I bougt a 95 volvo 850 turbo the other day and have started a bit of work on it.  Using your site I was able to retrieve(and clear) a check engine code of 315, and was wondering if you could tell me what it represents, and hopefully some suggestions of what to check to make it go away permanently.  

Second problem: I replaced the front brakes yesterday.  Unfortunately the rotors were rust-welded to the hubs, and I had a heck of a time getting them off.  The passenger side came off with some persuasion, but the driver side would not.  After a half hour of beating on it with a hammer I thought I'd take off the entire hub assembly.  I backed off the axle nut and then decided not to remove the hub.  I heated it with a torch and continued beating on the rotor and finally it started to budge.  Unfortunately since I had not tightened the axle nut, the end of the hub came with it. So I removed the nut and it came off.  At any rate I was thrilled it was off the car, and then was able to remove the part of the hub that came off.  My experience with these things are that they're supposed to remain sealed.  I cleaned the dust that got on the end and pressed it back in (no bearings came out).  Then I tightened the nut back on and everything pulled together.  My question is; is this acceptable, or should I bite the bullet and change the hub?  If I do, is it recommended to change both?

Thank you!

Answer -
shaun, definately change that hub, within a few weeks that thing will start making a hell of a noise.  I would only change the one side since its bad.  Wait till the other side starts making noise.  Roger

Answer
Shaun, yes, be careful on the front struts.  definately use quality spring compressors.  Also change the upper strut cushion while you have the strut apart.  I thinkg 3-1-5 is a knock sensor code but Im not sure.  I would have to look it up and get back to you.  Roger