We bought a TPMS system - Tire Minder TMG300C. We installed it for our four travel trailer tires, checked the pressure on the four trailer tires, and everything looked good. We drove about 200 miles, got to our site, detached the camper, and then drove into town for supplies. Here's what is weird. After detaching the camper, we drove for an hour with the TPMS monitor in the car and the TPMS monitor continued to show tire pressures for all four trailer tires! We were an hour away from the camper when finally ONE tire on the monitor started showing a "no signal" warning. Has this happened to anyone? How do I know whether the TPMS is really updating every 20 seconds like it's supposed to do so?