Glim is correct. Read the link. But to summarize: I accidentally discovered the pump low speed fault code in the ECU during another maintenance activity several months after it occurred. The first fault code showed up around 138,000 miles. I cleared them. The second instance of codes came up at around 145K (IIRC). I cleared them. Then the pump died on a 100 degree day about a month ago now, at 149,500 miles. The detail to all this is in the thread Glim referenced. I drive about 40,000 miles a year, so this all happened in the past 5 months or so.
My advice is if you discover the codes with a scan (using a BMW-compatible scan tool) change the pump soon after because it will eventually fail. I dissected my pump and can only surmise the failure is related to over-heated electronics. My pump spun just fine and the plastic impeller looked as good as new. The electronics smelled burnt. There was a fult code once the pump failed that said "Electronics - 77 Deg. C."
There is no warning when it is about to fail. It fails, the car overheats, the idiot lights light up. It's a great idea to have an electric water pump, but a poor design implementation on BMW's part.