Overheating

If the power-train control module detects that the engine is still too hot it will not escape limp mode. If you can feel that the engine is physically cold and the warning is still active, you could have an electrical or sensor issue, but for sure there was a coolant issue because your reservoir was low. I would have the vehicle scanned for trouble codes and go from there but there are a few known issues with this engine in particular related to coolant leaks, especially at the back of the head! I included a picture of the area in question.