I have a 2010 Nitro. The tpms indicates the monitor for the left rear is not working so I switched the rear wheels so that side had a known good sensor, and the left rear still has no signal. So I checked for a trigger for that wheel. I found out there are 3 triggers on the car and it uses process of elimination for the fourth sensor. The left rear is the one without a sensor. Anyone have an idea what the problem may be?