Hello guys, today i will be showing you how to diagnose a bad cooling fan on a 2010 335d
there are a few things you want to check
check all fuses related to fan
check for any shorts or ripped wires that go to the cooling fan socket as those can cause the fan to turn on
check voltage at the socket (what you get for the signal wire it doesnt matter, as voltage changes on the wire depending at what speed the fan needs to be so dont worry if you low voltage)
check the continuity of the cables (this is a better way to check for rips or shorts than simply unwrapping the cables and physically looking for shorts)


things to consider:
you may think you have a bad coolant temperature sensor. if the fan doesnt come on when you turn the A/C on then forget about the coolant temp sensor
you cant hot wire the fan to check if its good as the module on the fan has power all the time and providing outside power ( hot wiring it) wont do anything.
the last two things to check is the relay and fan, and the relay like i said in the video is $21 from FCP Euro and the fan is around $350 on ebay, so your best bet is to try to replace the relay first and if that doesnt do it then go ahead and replace the fan.

link for the cooling fan relay: https://www.fcpeuro.com/products/bmw...