For good measure I tested your theory. I wired it up with my battery charger, applied current, and watched it pumping coolant. It pumped with good pressure for a long time. It's impossible that the impeller exploded. Also, the noise is perfect - I can hear it perfectly because the car is not even on. Finally, I can hear the motor change speeds as I squeeze the main hose, essentially applying load to the impeller. This is enough data to conclude that the pump is working and in good condition. It's definitely the ECU/PBU or the relay. I suspect I burned it out somehow because about a week ago, I had a dead battery and connected the charger backwards to the battery (long story, but there was dirt and I thought he - was a +). Smoke came out of the charging cables, and the charger made a God awful noise. I quickly unplugged it, but alas, I am probably paying for that mistake. I have never done that in my entire life until now :-(