Found out there were several upgrades to the 2011 S Countryman N-18 temperature sensor/thermostat housing. Coolant leaking at temperature sensor was throwing the codes PO128 amd P173B on Arty. Thanks to Hagan we found that there was already one TSB upgrade performed before we purchased the vehicle. I believe it involved one sensor previously being replaceable actually being molded permanently into the thermostat housing. That left one replaceable sensor in an aluminum “L” in the coolant hose. This remaining sensor was leaking coolant into the wiring throwing these codes. A replacement sensor was not available (probably because they were discontinued due to leaking). We needed the next thermostat housing upgrade which has both temperature sensors molded into the housing as well as a different hose to replace the “L” and a wiring harness adapter for the new sensor location. Thanks to Alex, Evan, and Hagan at Century and Chris and Art at Head’s Up for helping insure the correct part numbers were ordered. Once we had the correct part numbers and parts then Head’s Up quickly got the car back on the road.