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

Nissan says in the car handbook that tire pressures should be set to 32
psi.

40 psi is a bit high and will give you a rough ride and not too good
handling in wet weather.


"BillGill" <billnews2 (AT) cox (DOT) net> wrote

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

Normally these systems use the difference in the rotation speed to sense
the low pressure in one of the tires. Not sure about this one in
particular though.

BillGill wrote:

BillGill wrote:
You might want to try a different gauge. The cheap ones are notoriously
inaccurate.

"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.

Butch
"AS" <donot (AT) spame (DOT) com> wrote

The company I work for manufactures tire pressure monitoring sensors and
receivers (among other things). I thought I would give you a brief
explanation of how they work.

The sensor is banded to the wheel inside the tire. There are different
flavours of sensors, but usually they are either continuously transmitting
or they have a switch inside that transmits only when the wheel is turning.
These sensors measure actual pressure inside the tire. They transmit via RF
to the receiver inside the car. The receiver is the "brains" of the system.
It will throw a warning when a sensor fails or when a tire pressure is a
certain percentage different from the others and/or it's initial value. The
sensors have batteries inside them and will last typically longer than the
life of the tire.

DS

"Butch Davis" <butch1277 (AT) earthlink (DOT) net> wrote

DS wrote:
I have looked the tires over, and looked on the web to
try to find out about the way the system works. I found
out that there are some that do work by difference in
rotational speed. At least some of these tap into the
ABS wheel speed sensor to check the wheel speed. If one
is significantly different from the others it triggers
the alarm.

There are several systems that use a sensor inside the
tire to measure the pressure. They typically transmit
the pressure to an on-board sensor for processing. This
is very similar to the set up described by DS. It
appears that the one used by Nissan is one that is built
into the valve stem. The sensor is actually located
inside of the tire.

I never did find anything that said exactly how the
Nissan system works, other than the integral sensor.
But I found at least one car that did have an over
pressure warning included. It was set to trigger at 39
PSI. That would be in line with my having gotten a
warning when my pressure gauge said the pressure was 44
or 45 PSI. Especially if my gauge happens to read high.

Some Nissan models do have the complete read-out on the
dash board display. The Versa doesn't, just the
pressure alarm.

I plan on getting a new, and hopefully more accurate,
pressure gauge. That should keep me better informed on
what is going on with my tires.

Thanks for all the good answers.

Bill Gill

Yes, difference in the rotation speed:
http://www.nhtsa.dot.gov/cars/rules/...ure/LTPW2.html

I made clear " Not sure about this one in particular though. "

Whose response is unhelpful and INaccurate?

Through the years I have come to realize that people who know the most
are mostly humble.

Butch Davis wrote:

"BillGill" <billnews2 (AT) cox (DOT) net> wrote

40 psi is too high. Check the placard for the correct pressure. Tire
pressures are often set higher than recommended for shipping. The
dealership should have set the tires to the correct pressure during
the pre-delivery inspection process.

The pressure will increase as you drive the car, so it is not
surprising that the pressure was higher when you checked the tires in
the middle of a trip. The pressures are to be set when the tires are
cold.

You also need to check your tire pressures at least monthly. As the
outside average temperature cahnges with the season, your tire
pressure will fluctuate as well. Don't put too much faith in the
monitoring system. I have a 2006 Frontier with the system. Like you
mine came on unexpectedly. I never did find a problem. I believe in my
case the system was triggered when we had an exceptionally cold
morning.

In my opinion, altering the pressure once the tires were hot was a
mistake. The front and rear tires ae loaded differently, so it is
entirely possible that they will have different "hot" pressures even
if they start out with the same "cold" pressure. You should set your
pressures to the manufacturer's recommended pressure when the tires
are cold.

The system only checkes the pressures once your speed exceeds 16 MPH.
I would not think a higer external emeprature would ahve triggered the
system since this should have raised the pressure in the tires.

Not sure. I belieev it monitors changes in pressure, not the
differential. In your case I think it reacted to the rear tires being
lower.

Did you check your owner's guide?

THe following comes form theon line version of the manual:

Low tire pressure warning light (if so equipped)

Your vehicle is equipped with a Tire Pressure Monitoring System (TPMS)
that monitors the tire pressure of all tires except the spare.

The low tire pressure warning light warns of low tire pressure or
indicates that the TPMS is not functioning properly.

After the ignition switch is turned ON, this light illuminates for
about 1 second and turns off.

Low tire pressure warning:

If the vehicle is being driven with low tire pressure, the warning
light will illuminate.

When the low tire pressure warning light illuminates, you should stop
and adjust the tire pressure to the recommended COLD tire pressure
shown on the Tire and Loading Information label. The low tire pressure
warning light does not automatically turn off when the tire pressure
is adjusted. After the tire is inflated to the recommended pressure,
the vehicle must be driven over 16 MPH (25 km/h) to activate the TPMS
and turn off the low tire pressure warning light. Use a tire pressure
gauge to adjust tire pressure to the recommended pressure.

For additional information, see "Tire pressure monitoring system
(TPMS)" in the "Starting and driving" section.

TPMS malfunction:

If the TPMS is not functioning properly, the low tire pressure warning
light will flash for approximately 1 minute when the ignition switch
is turned ON. The light will remain on after the 1 minute. Have the
system checked by a NISSAN dealer. For additional information, see
"Tire pressure monitoring system (TPMS)" in the "Starting and driving"
section.

WARNING

* If the light does not illuminate with the ignition switch turned ON,
have the vehicle checked by a NISSAN dealer as soon as possible.

* If the light illuminates while driving, avoid sudden steering
maneuvers or abrupt braking, reduce vehicle speed, pull off the road
to a safe location and stop the vehicle as soon as possible. Serious
vehicle damage could occur and may lead to an accident and could
result in serious personal injury. Check the tire pressure for all
four tires. Adjust the tire pressure to the recommended COLD tire
pressure shown on the Tire and Loading Information label to turn the
low tire pressure warning light OFF. If the light still illuminates
while driving after adjusting the tire pressure, a tire may be flat.
If you have a flat tire, replace it with a spare tire as soon as
possible.

* When a spare tire is mounted or a wheel is replaced, tire pressure
will not be indicated, the TPMS will not function and the low tire
pressure warning light will flash for approximately 1 minute. The
light will remain on after 1 minute. Contact your NISSAN dealer as
soon as possible for tire replacement and/or system resetting.

* Replacing tires with those not originally specified by NISSAN could
affect the proper operation of the TPMS.

CAUTION

* The TPMS is not a substitute for the regular tire pressure check. Be
sure to check the tire pressure regularly.

* If the vehicle is being driven at speeds of less than 16 MPH (25
km/h), the TPMS may not operate correctly.

* Be sure to install the specified size of tires to the 4 wheels
correctly.

-------

SYSTEM (TPMS) (if so equipped)

Each tire, including the spare (if provided), should be checked
monthly when cold and inflated to the inflation pressure recommended
by the vehicle manufacturer on the vehicle placard or tire inflation
pressure label. (If your vehicle has tires of a different size than
the size indicated on the vehicle placard or tire inflation pressure
label, you should determine the proper tire inflation pressure for
those tires.)

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. When the malfunction indicator is illuminated, the system may
not be able to detect or signal low tire pressure as intended. TPMS
malfunctions may occur for a variety of reasons, including the
installation of replacement or alternate tires or wheels on the
vehicle that prevent
the TPMS from functioning properly. Always check the TPMS malfunction
telltale after replacing one or more tires or wheels on your vehicle
to
ensure that the replacement or alternate tires and wheels allow the
TPMS to continue to function properly.

Additional information:

* The TPMS does not monitor the tire pressure of the spare tire.
* The TPMS will activate only when the vehicle is driven at speeds
above 16 MPH (25 km/h). Also, this system may not detect a sudden drop
in tire pressure (for example a flat tire while driving).
* The low tire pressure warning light does not automatically turn off
when the tire pressure is adjusted. After the tire is inflated to the
recommended pressure, the vehicle must be driven at speeds above 16
MPH (25 km/h) to activate the TPMS and turn off the low tire pressure
warning light. Use a tire pressure gauge to check the tire pressure.

* Tire pressure rises and falls depending on the heat caused by the
vehicle's operation and the outside temperature. Low outside
temperature can lower the temperature of the air inside the tire which
can cause a lower tire inflation pressure. This may cause the low tire
pressure warning light to illuminate. If the warning light illuminates
in low ambient temperature, check the tire pressure for all four
tires. For additional information, see "Low tire pressure warning
light" in the "Instruments and controls" section and "Tire pressure
monitoring system (TPMS)" in the "In case of emergency" section.

WARNING

* If the low tire pressure warning light illuminates while driving,
avoid sudden steering maneuvers or abrupt braking, reduce vehicle
speed, pull off the road to a safe location and stop the vehicle as
soon as possible. Serious vehicle damage could occur and may lead to
an accident and could result in serious personal injury. Check the
tire pressure for all four tires. Adjust the tire pressure to the
recommended COLD tire pressure shown on the Tire and Loading
Information label to turn the low tire pressure warning light OFF. If
you have a flat tire, replace it with a spare tire as soon as
possible. (See "Flat tire" in the "In case of emergency" section for
changing a flat tire.)

* When a spare tire is mounted or a wheel is replaced, the TPMS will
not function and the low tire pressure warning light will flash for
approximately 1 minute. The light will remain on after 1 minute.
Contact your NISSAN dealer as soon as possible for tire replacement
and/or
system resetting.

* Replacing tires with those not originally specified by NISSAN could
affect the proper operation of the TPMS.

* Do not inject any tire liquid or aerosol tire sealant into the
tires, as this may cause a malfunction of the tire pressure sensors.

CAUTION

Do not place metalized film or any metal parts (antenna, etc.) on the
windows. This may cause poor reception of the signals from the tire
pressure sensors, and the TPMS will not function properly.

FCC Notice:

Changes or modifications not expressly approved by the party
responsible for compliance could void the user.s authority to operate
the equipment.
This device complies with Part 15 of the FCC Rules and RSS-210 of
Industry Canada.

Operation is subject to the following two conditions: (1) This device
may not cause harmful interference, and (2) this device must accept
any interference received, including interference that may cause
undesired operation of the device.

--------

TIRE PRESSURE MONITORING SYSTEM (TPMS) (if so equipped)

This vehicle is equipped with the tire pressure monitoring system
(TPMS). It monitors tire pressure of all tires except the spare. When
the low tire pressure warning light is lit, one or more of your tires
is significantly under-inflated. If the vehicle is being driven with
low tire pressure, the TPMS will activate and warn you of it by the
low tire pressure warning light. This system will activate only when
the vehicle is driven at speeds above 16 MPH (25 km/h). For more
details, refer to "Warning/indicator lights and audible reminders" in
the "Instruments and controls" section, and "Tire pressure monitoring
system (TPMS)" in the "Starting and driving" section.

Interesting link. Did you not say " Normally these systems use the
difference in the rotation speed to sense the low pressure in one of the
tires?" Does "normally" not indicate that it is the norm? Does the norm
not indicate the usual? Did you not notice in the discussion of the ABS
based alternative that it does not work well enough at this time as it is
too inaccurate to detect pressure losses of at best 20% and more likely 30%
and that it has a set of additional proplems making it an unsatisfactory
system? For example it will not work at speeds over 70 MPH.

In order for the rotational speed of a tire to significantly change due to
pressure loss the loss must be large. After all, the tire circumference
determines the rotational speed at a given speed, eh?

Thank you.

Butch
"AS" <donot (AT) spame (DOT) com> wrote