Ok, so I have been getting an intermittent Tire Indicator and dash message on my 2007 DTS while driving on the highway during this lovely midwestern Wisconsin winter. I am getting Tire Pressure readings on 3 of the 4 tires and the other TP reads at --. Has anybody out there experienced this. It comes and goes. When it isn't malfunctioning all tires show as properly inflated at 33 psi. Seems like it is losing the signal from one of the tpms valve stems. Does anybody have a fix or an idea on how I can fix this problem or is this something I need to bring to a local tire shop and have replacement tpms units on rims? Thank you to all in advance for any advice offered or given.