I dunno what 4 sensor system that salesman was trying to sell you, but I reckon he's deliberately leading you up the garden path in an attempt to scare you with utter rubbish!! I've used a few of these TPM systems, in fact, most of those I've used have been 4 sensor systems (not all on trikes tho!) and NOT ONE of those 4 sensor systems ever had ANY issues running with just 3, 2, or even only 1 sensor sending info to the monitor/phone, just so long as the sensors not in use were turned off (or their battery was taken out)!! Sure, if you pulled them straight off the valve stems & just put them in your pocket while they were still 'on', the software responded with alerts about the loss of pressure or the low pressure they were reporting, but how many people wouldn't think of shutting those sensors down when they took them off the valve so they didn't report at all?? Or simply not turning them on in the monitor if you didn't/weren't going to fit them??? You might hafta turn off the 'no signal' alert or the warning that the sensor there isn't working once, but once done you won't hear any more from it until you change that! My current 4 sensor Tyre Dog TPMS is working fine on my 2013 RT without the 4th monitor on or showing, & I don't get any alarms about of from that 4th sensor.
So I'm reasonably sure that you shouldn't have any issues running just 3 sensors of most 4 sensor systems, just so long as the 4th sensor isn't in your pocket or dumped in the frunk & still turned on/set up on your system. :thumbup:
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