Fan Sensor

I have a 2003 Honda Civic EX 1.7L V-TEC with about 106,000mi, OVERHEATING These are the steps I have taken to get to this point. When it first started about a couple months ago the temp. Gauge would shoot up and shoot right back down so I pinpointed that the thermostat was sticking, so I replaced it. About 2 weeks later it started overheating again at first it would do it just a little every now and then then as time went on it did it more often and got more hotter. I forgot to let the air out of the coolant system when I changed the thermostat so I did that and again it ran fine for about a week and a half, then once again it would start slow and do it more often and hotter with time. So I thought it was the cap not holding enough pressure and air was getting inside the coolant system and causing it to overheat so I went and replaced that. Well now I've noticed it really only overheats when the car is goin slow or at a stop and im not hearing the fans coming on when they should so now my new target is the fans. On my car there is a sensor right next to the thermostat which im pretty sure is just for turning the thermostat on and off because the guy at the dealership said the fans have thier own sensor, so I have ordered the fan sensor and would much appreciate some help on locating this sensor and a little bit of a walkthrough if possible. THANK YOU! Kevin