According to the generic fault code you have stored it says you have a bad coil. You have swapped the coils from one cylinder to the next and you still are getting the same results so that says your problem is still in that cylinder, regardless of which coil you put in that hole.

Now if we stop right there and assume that the code is right on the money then we can deduce that the coil is in fact good and it is just not being driven by the Motronic control unit. But, before I blew the wad on a control unit I would diagnose it further and make sure that you have absolutely everything else necessary to make and sustain combustion in that cylinder.

On a basic level you need fuel, spark, and compression all delivered in the right amounts at the right time to make this happen. It would appear that the other 4 cylinders seem to be getting all of this so your problem is unique to this hole and not something that they all have in common like a faulty fuel pump or something like that.

The generic fault code specifically says "Ignition Coil B Primary/Secondary Circuit Malfunction", that does not leave a great deal of wiggle room on the interpretation. You have a problem in the primary or secondary circuit, you replaced the coil and it is still there so you can rule out the secondary circuit and go with a primary circuit problem. The primary is that which turns the coil on and off, that would be the control unit or the wiring in between.

Now like I stated above you should really rule out all of the other stuff and make sure that it is the control unit. To do this you should perform a compression check, do all 5 cylinders, and swap the injector from one hole to another. At this point you will have checked the basics; spark, fuel, and compression.

The control unit has drivers for both the injector and the coils and it monitors the operation of both. When it sees something irregular in one of them it will post an appropriate code that will designate which cylinder and which system (fuel or spark) is malfunctioning.

The pressure release valve for that should be on the end of the fuel rail, left hand side, and it should look like a schraeder valve. Unscrew the cap, stick something in there to depress the valve and bleed it off. It is just like letting the air out of a tire.

Hope this answers your questions and clears it up a little bit.

Mark