For all the hype and considerable amount of space which has been consumed by this problem on UK Whitegoods, there is still much confusion and unnecessary posting about what is usually a straight forward problem.
E2 specifically means that the water level safety system has been activated. In plain English, this means an overfill, and the secondary water level switch has been activated.
To explain the problem fully, a brief description of how the fill system works follows.
Water is introduced to the machine via a solenoid controlled water valve. This valve is normally mounted to the rear of the dishwasher and the water inlet hose screws directly onto it.
This is switched initially by the computer board ("Timer" in SMEG-ese) or control module, which is this type show here.
The water is routed through a fill matrix on the right hand side of the appliance.
This contains various channels and chambers which may be filled as the programme requires; the rest of the water being allowed to run down and through a transfer tube into the sump of the machine (the area covered by the filters).
As the water level rises, air is displaced from two "collecting chambers". One of these acts as the displacer to the water level control switch, the second is the safety, or overfill switch. The switches are operated by air pressure.
The problems arise because food deposits build up initially in the transfer tube, and latterly in the fill matrix itself. This restricts the free flow of water into the machine and causes water to back up and operate the safety system. There is no circulation pressure in this particular water circuit, so there is nothing to wash the detritus away.
This picture shows the bottom of a typical Smeg dishwasher side fill chamber and this is where it gets all gunged up
In my experience, 9 out of 10 instances of the dishwasher's E2 problems can be solved by identifying the transfer tube and cleaning it out.
Looking into the sump area without the filters, you should spot a tube with a black rubber flap at the end. This is the one to be cleaned out.
Methods which have been discussed include long stout Tyraps, skinny long-handled bottle brushes and blasting water or air down the tube through a fine hose. The net result is a surprising amount of crud arriving in the sump of the machine. This is actually a good sign as it indicates that deposits are being removed.
However, on occasion, the fill matrix itself can become choked. It can be removed and to our certain knowledge people have used garden hoses, even jet washers to try and dislodge the goo, with varying degrees of success.
The only guaranteed repair at this point is to replace the matrix and ensure that crockery is rinsed of any heavy detritus before washing to ensure that there is no repetition.
Other possibilities are faults with the pressure switches and leaks in the air pressure system, or excessive water flow rates. These however are exceptional cases and need a technical solution; engineer time.
Needless to say, any repairs or inspections should be carried out with the power OFF
If you unsure of any of the components or instructions in this article then DO NOT ATTEMPT TO REPAIR THIS YOURSELF please call an experienced dishwasher engineer.