water pump fuse or relay? pump not working at all Aug 13, 2016(read on here some where that if the water pump is not working the fans will turn on immediately upon start of the car). Left the car running to see if it would over heat and eventually it started overheating. So I started checking all fuses and found the 40amp fuse in the eco box was blown. replaced the fuse and everything is perfect now. Fuse and relay box diagram BMW E90 - fusesdiagram Fuse and relay box diagram BMW 3 E90. Identifying and legend fuse box.