Remove the upper and lower body panels, disconnect the main battery interconnect cable, it's the big red cable that leads to a blue connector that goes into the frame, this is the power cable that attaches the upper and lower battery packs together, you want to do this before working on anything electrical for safety. Under the lower bodywork at the front is a black rectangular box with the electrical connector attaching to the right side of the converter, this is the DC/DC convertor. If the converter hasn't failed completely, this connector is the most likely problem, contacts are probably dirty or the connector has worked loose somehow. Separate the DC/DC electrical connector and clean the connectors on both ends, for this I just sprayed some WD40 in both ends, blow out excess, this next step is probably the most crucial, on the female end of the connector you want carefully push or pry both sides of the female contacts closer together, do the same for all 4 slots, reconnect and disconnect it a couple of times, recheck the female connector and readjust the contacts if needed then reconnect make sure the connection is solid and it wont come loose. Reattach the battery interconnect and the power tank button if you have one and the bike should power up normally, if all works as it should, button back up and your good to go.
I had same problem on my 2010 Enertia for months, I'd clean contacts on the DC/DC connector only to have the V58 error code popup again, could be days or weeks but it would always comeback, it wasn't until I made the the contacts on the female side of the connector tighter so it would apply more physical pressure to the contact points finally solve the problem. Hope this works for you. Good Luck!
