I haven't seen this one, and I just went through it, so as my feeble contribution to the knowledge-base we call the Internet, here's a little story.
Last night, my son came to me complaining that his water tasted funny. That's how most things start around here. What he meant was that he could still taste the apple-juice in his sippy-cup. Being the good Dad that I am, I took apart his cup, smelled the juice, and got him a fresh one.
Our dishwasher (4 year old Bosch 3300/SHU) was running, so I opened the door, waited for the dripping noises to stop (I know, you're supposed to push the on/off button first, but I hand't read the manual at that point :) chucked his apple-juice tainted cup in, and started it again. The machine burped, then went into its drain cycle. Drat, I thought, must have been at the end of the wash. 10 minutes later it was still making draining noises, but not actually exhausting any water because, well, there was none left.
At this point even my wife noticed that things weren't completely right in the kitchen. Accusing looks were traded amongst all parties (except my son who was happy with his new water cup). So I switched it off at the on/off switch, and said something like "I think I broke the Dishwasher". Not a smart thing to say it turns out, since money has been rather tight since I've been out of work for over a year.
However, I'm a handy sort, and I figured that it might be possible to diagnose and fix it myself. This is 8 at night BTW. So, the first thing I did was go dig out the users guide. Not much help there, this was not a failure mode that they hadn't forseen. One more time for good measure in case it magically fixed itself, switch on, hear the pump, press all the buttons at least twice, no change. Off again. On again. Off Again. Unplug. Plug in. On again. No change. Still furiously pumping air. Sigh.
So I started with the cleanout procedure. Hmm. Didn't know you're supposed to do this every month. Lets see, 48months old, 1 cleaning about to occur, well better late than never eh? Unscrewed the plastic bit with the 'microfilter', slid out the metal filter. It's all covered in some white sludgy material. Some of it has gone rock hard. Well I guess we do need to clean more often. Picked out all the ex bits of food which haven't dissolved in 4 years of nightly exposure to almost boiling water (the end-bits to Avocado Pears mainly) and some more of those rock hard white things (have you been stuffing teeth down this thing?)
Put some water in, try again, drains the water, doesn't stop. Ah look, there's a torx screw that looks like I might be able to get off without destroying the machine. Maybe something under that plastic cover it's holding on is responsible for the problem. Out comes the screw, off comes the cover with a bit of rocking and tugging, and more of that nasty white stuff. Some of which looks quite 'fresh', namely that when you crunch it with your thumbnail, it has crystalline power inside.
White crystalline powder? Hmm. Under the cover is what appears to be a little impeller, probably the drain-out pump. Nothing obvious here. Put it all back. By now I'm becoming convinced that there must be some limit switch in the machine that senses water level in the sump, and that somehow that has got stuck. Where would a schematic be. Inside the machine? Probably. Pull off the base-plate, pull out the machine, look around, everything looks good, ah, there's a folded up piece of paper that says "Wiring Diagram". Lets take a look.
Yep, it's a wiring diagram. Shows all the bits, but not where they actually are. Completely useless for this task. Well at least I know there's nothing useful I can do under here, so I put it all back together again.
Next, (should have done this first I guess), onto the Internet. No direct hits on this particular problem -- which is why I'm documenting it here --, but lots of advice including how to rig the door-switch so you can watch the machine working while the door is open. A piece of my advice here: don't do this with any substantial amount of water in the sump unless you plan to wash the entire kitchen afterwards, or you can slam the door closed very very quickly :) And wear safety glasses: I always do and last night it paid off when the machine shot a blast of water vertically into the roof of the chamber, and everywhere else including my head.
The one thing I did pick up on was that you should periodically consider doing a Citric Acid crystals cleaning of your machine if you are in a hard water area. Well, our water is so hard the ducks walk on it. But I didn't have any Citric Acid crystals to hand, being about midnight at this stage I didn't think I was going to go out and get any. But, I did have a bottle of CLR: (Calcium Lime Remover?), and it works great at getting rid of limescale buildup. What the heck, I thought, last chance, chucked quarter of a bottle in the sump, started the machine, and I swear it immediately switched from drain to off.
AAARRGGH! I broke it for good now I thought. Quick, open the door and chuck a bucketfull of water in. Heart pounding, my wife will kill me when she finds out I really broke the machine. On again, machine pumps, then stops like it should. Huh? It's working again.
Then it struck me what the white gunk was. Dishwasher powder. When we started the cycle earlier in the day, the little door that hold back the powder had flipped open when my wife closed the door, and it had emptied all onto the floor of the machine. She asked me "will this be ok" and I said "sure". Nope.
What appears to have happened is this. The powder sat around at the bottom of the machine, forming under moisture and heat, a rock hard/sludgy substance that sank into the sump of the machine when I stopped the cycle. This then appears to have gummed up the float switch (I still don't know where this is, but it's on the wiring diagram, and presumably somewhere in that sump), causing the dishwasher to keep pumping because it thought the sump was full. The introduction of CLR is like hot-knife-through-butter to dishwasher powder, a fact I verified by mixing the two on a dish and seeing lots of vigorous foaming.
Once I throw the CLR in, it dissolved whatever was holding the float switch in the "float" position, and let the machine complete its cycle.
So, a long story, but something to try if your machine ever gets into this mode of misbehaviour.
Hope it helps.