Sync and Drive throw codes but no check engine light and diagnostic tool does not pick it up

I came here looking for an answer for this same issue. A couple of years ago Sync showed me a trouble code. I took the car into the dealer, they said their machine showed no active or stored trouble codes. … Earlier this week Sync sent me a trouble code that said "Coolant Thermostat Malfunction" "Coolant Thermostat failed, replace" but there were no warning lights on the dash and the gages looked fine. … I took it to the dealer and was told that their machine didn't see any active or stored trouble codes but they replaced the thermostat anyway because it's covered under the warranty and would rather be safe than sorry. (Guessing since I showed them that code had popped up and they didn't replace it then the engine overheated and had to be replaced they'd be liable?) On my way home from the dealer, the same code popped up. Still no warning lights on the dash, gages still look fine. … AND I missed a wedding I was planning to drive across country for due to the car being in the shop when it might not have even needed to be.

Posted elsewhere also

Bad experience with SyncUp-Drive --  Worked satisfactorily for 5 months.  (A couple of modest issues, like not being able to clear old trips.  Want only 7 days, erase older.)  MAJOR issue started in August with FOUR Engine status codes.  Took car to shop.  They confirmed the same codes with Professional Diagnostic Tool.  Afterwards, reinserted Sync-up Drive.  Never was recognized.  Most recent info (car location) shows still at repair shop.  Still shows the 4 error codes.  Lacks detailed instructions for users who like to dig into the weeds.  TMobile (corporate) Store personal tried to help, discovered internal doct revieling a reset pin.  Tried that, no joy.

I also came here looking for answers? But unfortunately found none so disappointed, I also had a dtc code saying that my thermostat wasn't working properly, it said coolant temperature below thermostat regulating temperature, with no checking engine light on, but I didn't want to drive being nervous, I took it to get checked, after taking the car to several places for them all not to find nothing,  iam driving a few days later the check engine pops on, so I take it to the mechanic they check it again this time and indeed it's the thermostat, so I get it replaced $$$ 🤨, so it's replaced and you think everything is okay, NO or I don't know because the code won't go away from the previous day. It keeps showing the code error from 3days ago and time it happened,  but it's a brand new thermostat,  with a 3day old code and time still showing on the sync up, no check engine though, i was going to take the car out of twn but being nervous I took my other car, I fear breaking down on the turnpike, needless to say what's going on with this sync up 🤨, please help if you can thanks.