I have a 2017 Model X. The Coolant Heater was just replaced. The reason mine was replaced was due to the following error messages that came on vehicle screen. (1) Vehicle may not restart - Service is required. (2) Acceleration and top speed reduced - Performance may be restored on next drive. All these was the day before Thanksgiving. Reported the issue via Tesla App. I was scheduled for the following week Friday. Because of the message that the vehicle may not restart I didn't drive the car for the next few days until I spoke with Tesla the following week Monday. Tesla SC actually called me that Monday morning. They asked if I could bring the vehicle in the next day because they fear the vehicle may actually die-out before Friday (my scheduled service date). Tuesday morning at 9AM I dropped off the vehicle, they had a loaner MS waiting for me. At 3:45PM same day, I got a call that my vehicle was ready for pick up. They had replace the Coolant Heater and they also updated vehicle software to maintain compatibility with Tesla connectivity network. I didn't even know that the software for network needed an update. BIG KUDOS to Brian Griffin (Service Advisor) and the Service Technician (I don't know his/her name) at Tesla Service Center, Superior, Colorado.............I'm very pleased with the service I received from the SC.