Code 15 Coolant sensor circuit

My check engine light came on so I checked the code it was 15. The book says that indicates a problem with the coolant temperature circuit on my 1994 Metro. The temperature guage seems to work fine. On an 85 degree day the engine warms up in just a mile or so then sits about half way between hot and cold. So unless the ECM uses a different sensor than the guage I think the sending unit is ok. The next thing it says to do is check the wireing to the ECM. Do the guage and the ECM use the same sensor? Where is the ECM and what does it look like?

I found an answer that said reset the code (pull the taillight fuse) disconnect the CTS and recheck the code if the new code is 14 the sensor is bad if it still says 15 when it is disconnected the wiring is bad. Mine said 14 so I bought a sensor. I have not installed it yet.