2006 Volvo d12 egr valve cleaning?

I have a 2006 Volvo with the d12 and im getting the egr valve ecu code. I was planning on buying the valves and replacing myself in the next day or two but before I do I was wondering if its possible to clean them and try that first. it looks to me that if I take off the square cap that would get me access to them though I don't know. or is that even the issue when these things go bad? Also if I do open them up and try to clean them and it doesn't work will they still take them as a core? Just the core charge on these things are $850 a piece. Any help or advice would be greatly appreciated. Or if one could direct me to a step by step on how to bypass them. Thanks in advance for your help