P0115 is a trouble code for the coolant temperature sensor.  A scan tool
which reads engine data will be a great help in determining whether the
sensor or some other component is the issue.  Typically, the problem is
the sensor.

I've got code readers on the brain. Please tell us what code reader
you're using. I'd like to know your experiences with it, too.

Please give more information in your posts (and make sure to write
clearly -- use punctuation, capital letters, etc.; I cannot make out
what you are trying to say). For example, we need to know  why there's a
discrepancy. What kind of car do you have? Why is the CD giving you an
answer you think is false?

FYI: the Hyundai codes are all defined on the Hyundai technical web
pages (sorry, I don't have the link handy, but I'm sure someone else
here will provide it for you).

My experience with two consumer code readers so far is that they vary in
"friendliness." In fact, when it comes to Hyundais, I would rather that
the tool is not provided with pre-progammed code explanations, but
rather just displays the code designation for me to look up. I don't
trust that the definition provided by the manufacturer of the code
reader is accurate, but I do trust that Hyundai knows the meanings of
their own codes. I recently returned a code reader from AutoXray because
the user interface was so klutzy and inhuman that every time I turned it
on, the thing made me angry. Part of my reaction was due to the
frequency of messages that said, in effect, "We know that there's a
problem here, but we're not going to tell you what it is unless you send
us money for an upgrade." I sense a certain amount of what amounts to
extortion going on in this business.

Richard