The reason I ask if you had cleared the fault code is that it may be an old fault thats been fixed. Usually one makes a note of the fault code then clears the fault, take car for a drive then recheck to see if the fault code returns,clearing the fault code wont fix the problem. The solenoids are fitted in the valve chest, there is a wiring loom inside the box that connects to all the solenoids which may also be suspect