Outside temperature gage fluctuates

Sorry I don't know the answer to your question about the outside temperature sensor. Unless there really was some much colder air/wind out on the road compared to your 55 degrees at home then I suppose it must be a sensor issue.

I'm pretty sure however that the yellow light is just the "snowflake warning" isn't it. I think it's just to warn you that you cold potential strike and icy patch, not that the engine can't cut out.

 

It is possible this is caused by corrosion on the connectors to the sensor. The sensor is mounted in front of the radiator on a vertical support and is easy to get at. The sensor does feed OAT to the engine ECU but I do not believe it will affect how the engine runs to any great degree.

There have been obscure reports of the temperature misreading but this is usually reading high because the grill is blocked (for winter) or the aircon fans have been installed the wrong way round after damage repair.

 

If the temperature sensor gets wet, it will get colder than the actual temperature. Depending on how low the relative humidity is, it can get a lot colder. Don't ask how much -- I'm not that bright. If it was raining or you were driving through puddles, this could be normal behavior.

 

Sometimes connections get dirty and may cause a problem like the one you are having. I recommend you locate the sensor, unplug it, and clean the connections with QD electronic cleaner. Most auto part and hardware stores have it (at least around here, anyways).