Cheers buzby. Im going to buy a code reader off ebay but unsure of what type would work?
The one mentioned in that link to the other forum is a generic ELM337 ODBII interface - you can get a USB version to connect to a laptop, or a Bluetooth version to connect to a laptop or smartphone. You will need software on the laptop or phone to do the code reading and resetting - I'm not sure what is available for Volvos on laptops, but the person on that forum was using the Android Torque Pro app.
The system Volvo dealers use is a set of applications called VIDA, and they use a bespoke USB/Bluetooth interface called DICE. These are available to buy from Volvo but cost a fortune, and you also have to buy a subscription to use VIDA (as it checks in with Volvo's server when you start it up), which again costs a fortune..
You can buy cloned DICE interfaces (the clones only have USB) that are usually supplied with a hacked version of VIDA (it doesn't connect to Volvo's server, which subsequently reduces the functionality). There are a lot of software prerequisites that need to be loaded onto the PC to get VIDA running (you have to be running the right version of Windows, the correct versions of the .NET framework, MS Access client framework etc) so it can be a bit of a pain to get it running. I have the 2013 version of VIDA running on an XP Mode Virtual PC but I only got it running after the 3rd install DVD from 3 different suppliers (the first 2 discs had been burned from corrupt image files).
I don't have a DICE unit though (my car is still in warranty, and the car logs every time DICE connects to it - a genuine version of VIDA logs it on Volvo's server as well). I just use VIDA for the parts database, and disassembly and repair instructions.