"Difference in rotation speed"? Want to think about that a little? According to the little bit of physics I've learned your response is unhelpful and unaccurate.
If you take your Nissan to a shop with the right reader the pressure in each tire down to one decimal point can be read. The reading is very accurate, too, BTW.
The problem is in one or more of the tire sensors or in the reader/indicator module which triggers the instrument panel indicator.
Typically shops don't like to spend much time on diagnosing LTP warning malfunctions. My local dealer's service manager stated that he wished they had never put the damn things on the cars. According to him about 99% of the warnings were due to owner inattention to TP or to improper pressure adjusted by owners.
Last week, after the third time in the shop for my low TP indicator malfunction they reset the receiver/indicator module instead of simply adding air. Hopefully this will do the trick.
Normally these systems use the difference in the rotation speed to sense
> the low pressure >> I have a brand new (bought in January) 2007 Versa. When I got it the
>> tire pressure on all 4 was set at 40 PSI.
>> I have left it at that value since the dealer/factory set it.
>>
>> Last Friday I took a short road trip, less than a hundred miles. About
>> 2/3 of the way there the Low Tire Pressure light came on. I immediately
>> pulled over and checked the tires. None seemed to be low, so I got out
>> the pressure gauge and checked them. I found that the 2 front tires were
>> up around 44 or 45 PSI. The rear tires were still around 40. I reduced
>> the pressure on the front tires to 40 and started on down the road. The
>> light went out and has stayed out ever since.
>>
>> I have made that trip twice before since I got the car but this is the
>> first time when the temperature has been in the 70s. The last 2 times it
>> was much colder.
>>
>> Does any body know what could have caused that? Does the system check
>> more for a difference in pressure, rather than an actual pressure? >>
>> Thanks for any help
>>
>> Bill Gill