 Overheating, low speend fan not grounding?
Background: Car overheated into the red this weekend. My wife got out and noticed the fan wasn't on. She said soon after the fan turned on and cooled down enough to bring the temp down.
I checked it out that night and the cooling fan wouldn't turn on (it works with the AC). The car got to 3/4th after light reving and the fan wouldn't turn on so I shut it off.
The car always ran just a bit hot so I decided to send it to a local bmw shop. I had a waterpump/thermostat laying around so I had them put it in. I asked them to look it over and also check the fan switch.
What they found....
They said the fan switch was working just fine. However, it wouldn't turn on the low speed fan. They said the ECU wasn't getting/receiving a ground signal for the fan.
Questions:
1. When should the high speed mode kick on, I think it should be before 3/4 temp.
2. What would be causing the fan to not work if the fan switch apparently is fine?
Thanks for the help, they are going to look at it tomorrow some more but if the fan doesn't come on it is just going to overheat again. Any help would be great! | 
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