I removed the drain pump, pulled out the sump assembly, transferred the turbidity sensor and the other wires to the new sump assembly, put it back in, and reattached the drain pump.
This is the third time I have replaced the circulating pump on my several year old KitchenAid dishwasher. This time, I decided to replace the entire sump assembly because the pump itself was about the same price (and I could salvage some other spare parts just in case).
Because I was concerned about the water level and some other details, I also removed and cleaned out the inlet valve, so in my case, it took longer than it strictly needed to take.
It would be nice if the impeller were available separately from the motor -- in all three cases on this dishwasher (and twice on a previous KitchenAid dishwasher) the pump impeller failed (the brass thread on the plastic impeller that connects to the motor shaft either came loose from the plastic impeller or the threads connecting to the motor shaft stripped out, and the impeller either just sat there while the motor ran, or wedged the motor in a way that caused it to burn out). I think it would add maybe 15 or twenty minutes to the job to replace the impeller (what should be perhaps a $10 part) rather than replacing the circulating pump, or less than an hour more than replacing the entire sump assembly. A better-built motor (or at least one not designed so it should be allowed to cool 10 minutes for every 20 minutes it is run -- on a dishwasher that frequently runs it for quite a bit longer than an hour straight) and better impeller would make these things much more reliable.