Whirlpool APDW/2 drain pump runs continually till it times out with error?

I have a Whirlpool APDW/2 integrated dishwasher that starts the drain pump which it runs till it times out and then the start LED flashes in a sequence of 4 flashes. The unit never starts to fill. The pump became very noisy before it eventually stopped working.

I have had the drain pump out and the impellor is in tact and free to rotate. If I pour water in to th emachine it is pumped out and when I powered up the pump whilst it was out the impellor turned. The only thing I noticed is that the coil sounds like it is arcing. I am pretty sure I have had this before on a previous identical unit I owned but I can't remember if it exhibited the same problem.

Can anyone translate the error code for me? Can't find a list on the web anywhere. I think it could be a faulty drain pump but before I fork out for a new one I thought I would ask for advice here.

Cheers