I got the P0597 "thermostat heater control circuit open" OBD diagnostic trouble or fault code (DTC) last month. There were no leaks that I could see and we pretty much avoided driving it until funds permitted me to buy the parts.

The 2012 Cooper S hatchback can have one of 2 different styles of thermostat covers with one of 6 variations of plugs. There is also a design change from the original that changes the type of temperature sensor with a new "Y" cable adapter and a new overflow tank to thermostat hose.

I pulled a youtube video of a R56 and it was almost the same with a few minor changes. This is a PIA job. It took me 2.5 hours to get the thermostat cover out but I labeled all connectors and took my time to make sure I did not miss anything or break any of the little plastic catches and clamps.

I got my parts from Way Motor Works just inside the perimeter in Atlanta. He explained the updated parts and told a few thing to look out for. A big THANK YOU to WMW.

I spent 3 hours putting it all back together. The part I thought I was going to have a problem with was the metal clip that holds the heater tube on on the back bottom side. Way told me to be sure to put this on first. I couldn't get my big gorilla hands back there so I took a piece of 1/4 copper tubing and flattened out one of the ends a little bit. I then ran a loop of string through it so I could side top of the clip in the flattened out end. I was able to thread it past the hoses and other items in the way to snap it back into place locking the hose to the housing. I then let go of one of the end of the string and pulled the other through and removed the tube. It was actually easier to get back on than it was to get it off.

Other than that everything went back together without a hitch. Again many thanks to Way Motor Works.
https://www.waymotorworks.com