I received the 'dread' P1688 - but when reviewing the various threads, it is often accompanied by a number of other fault codes and usually the poster is stating that the engine won't run. My CEL came on ....but other than a code that can be reset (engine off) - but returns when engine is running - the truck drives and the VP pumps. I expect I will have to replace the VP.....but I don't want to rush and replace it if there might be something else to check and maybe something else might be the