08 XLR-V,, "service fuel system" in DIC and gas gauge says empty, this happened with about 1/4 tank. Filled it and added some fuel system/injector cleaner as well,, nothing changed. It seems like I read this is because of a stored DTC code? And "clearing"? the codes might correct it? if only for awhile? If so, how do I clear any stored codes???? unhook battery? if so how long?