Originally Posted by jsr72
Isn't that true only for indirect systems?
Technically from version 5 of the 12 owners guide pg. 245:
As an added safety feature, your vehicle has been equipped with a tire pressure monitoring system (TPMS) that illuminates a low tire pressure
telltale when one or more of your tires is significantly under-inflated.
Accordingly, when the low tire pressure telltale illuminates, you should
stop and check your tires as soon as possible, and inflate them to the
proper pressure. Driving on a significantly under-inflated tire causes the
tire to overheat and can lead to tire failure. Under-inflation also reduces
fuel efficiency and tire tread life, and may affect the vehicle’s handling
and stopping ability.
Please note that the TPMS is not a substitute for proper tire
maintenance, and it is the driver’s responsibility to maintain correct tire
pressure, even if under-inflation has not reached the level to trigger
illumination of the TPMS low tire pressure telltale.
Your vehicle has also been equipped with a TPMS malfunction indicator
to indicate when the system is not operating properly. The TPMS
malfunction indicator is combined with the low tire pressure telltale.
When the system detects a malfunction, the telltale will flash for
approximately one minute and then remain continuously illuminated.
This sequence will continue upon subsequent vehicle start-ups as long as
the malfunction exists
Basically its only meant to show a gross under inflation but otherwise you're supposed to pay attention. Its really only a legal cya for the manufacturers mandated by the government.
As long as it doesn't tell you the actual pressures its pretty much useless for monitoring anything except a catastrophic failure.