what is that 21mm sensor plugged at the bottom driver side of the radiator. i had to remove this sensor since the wires broke.

 

Coolant warning buzzer if the level gets to low?

 

It's a temperature sensor... one of at least three that I know of on the car. I assume it's function is for the ECU like the one by the thermostat but honestly, I'm not sure.

 

That big guy is for the cold start assist

 

Ahh, that's the thing that is broke off mine I think...

 

cold start assist? mine starts fine. it does smoke alot though.,

 

from what i understand its the coolant temp sensor... the s5's have it on the back of the waterpump housing

 

It's the water temp switch dedicated to the Emissions system. It controls whether or not the air bypass solenoid opens for 17 seconds during cold engine starts and is also used to control to some extent the Relief Solenoid which in turn controls when the ACV dumps air overboard instead of into the exaust ports.