Id first up clear any logged error codes by removing the negative battery terminal for a minute or two, and then recheck the error codes again after an hour or so of driving the car again, as this will show if any logged errors are still occuring, because sometimes error codes will set due to a one off "glitch" or whatever, so its wise to make sure theres actually a problem there first. If the code comes back again after clearing the codes and driving the car, then check the wiring and connector to whatever sensor the code points to, (in your case its the coolant temp sensor), so check its wiring and connetcor. If the wiring and sensor connector are clean and tight, and the code still continues to set after being cleared, then replace the sensor as these can wear out and fail just like any other part.
