My roadster is stored for the winter and I started it today and backed it out into the driveway to idle and warm up to temp. I noticed the TPMS light was on and the rear right tire read 25 pounds. I topped off all tires to 30 but the light is staying on of course. I understand a few miles of driving is needed to complete the reset function but that will not be possible as Rosie is only covered by comprehensive during the winter months so driving it is out of the question right now.

My question, is 25 pound enough to trigger a light or after 8 years are my batteries finally starting to croak? I'm leaning toward the latter. I have read where 180 says we should get 10 years out of these but nothing is ever cast in stone.

Thanx guys!!

 

There isnt much give for the light, I think it's 31 and below it will kick on. The door says 32 up front and 33 out back I believe... and that is for cold setting.

 

Thanx. A search on kick on pressure came up empty for me so your input is appreciated. It is single digit temps right now so I was reluctant to crank the tires all the way up. I will just wait for spring and warmer temps, set the pressure to the rated amount and see what happens.

There is always Rudy's #2 wire removal to make the light go out if all else fails. I believe that to be legal as Federal law mandates all >10,000 GVW made after 2007 have the system and be operating. Mine of course is an 05 so TPMS then was a luxury, not another mandate by the nanny state.

Thanx again.

 

The pressure where the light comes on is one or more tires 25% below the normal tire pressure. This is stated in the Owners Manual. Cold weather can drop the pressure a couple of PSI, using the car the pressure will increase by 2 to 6 psi.
When the light comes on in cold weather it means the tire pressure was low before the cold temp, the cold did not drop it by 25% as some people think, just enough to reach the 25% less condition.

I'm sure that the 25% is an approximate number, but 25% of 32 psi is 24 psi.

Make sure your tire pressure gauge is accurate as many are not too great at all.

 

No problem... Once the cooler weather started here I was in the same boat, confused. I stumbled across a thread with someone speaking percentages, equaling out to about 1 psi or something like that. All I know is that above the 32 mark my light goes out. Like you said though, its cold enough where you are it's hard to say what should be done.

 

If that is the case, then yeah... My sensors are bad lol.

 

Shoulda read the book. When all else fails, read the instructions.

I have a real old WW Grainger tire gauge. Yes it has WW in the name that should say how old it is. Prolly time for an upgrade.

Thanx again for all for the input. In 5 months I will get to the bottom of it. Until then Happy Motoring & Happy New Year to all.

 

My tire gage is a bit old as well.
Not too accurate is my guess. LOL
Patented in 1914

 

OK, just a lil cornfumed here... I was led to believe the TMPS sensors activated (transmitted) when the centrifugal forces resulting from the rotation of the tires while driving acted on the switch and if the pressure was (as stated earlier) 25% below setpoint, they indicated on the dash that one of the tires (could even be more than one) was low. So, if this is true, how does a signal transmit if the car is in storage (not driven)? I just get so cornfumed.....

 

Your first patent Dave?

 

The same way it transmits low pressure when the temps drop to 17 degrees and you first start your car..

 

Turn on something controlled by a computer and it will not go off until the computer signals it to turn off.
Two simple commands, ON (1) and OFF (0) control our lives these days.

 

OK, Page 216 of the 08 owners manual has a rather large box bold typed "CAUTION!" in the left hand 'column'. In the box it describes (kinda ambiguously) the TPMS ans the light in the dash. Last sentence states The vehicle needs to be driven above 20mph in order for the TPMS to receive the information. In totality, the cautionary statement leads you to believe the tire will transmit (with a nominal system) when the wheel is (going) the equiv of 20 mph or above. So, is the manual not descriptive enough? I'll now delve into the service manual and come back!


I JUST LOVE THESE SERVICE MANUALS! With that said, page 22-60 of the 08 service manual set titled SENSOR subset OPERATION (lower page) Para 3 states (in totality) the sensor sends a signal only when the tire is rotating at an approximate speed of 20mph (nominally). I am sure the other various manuals will have the same information located in there UNLESS different year models use a different model sensor pack (of 4). This makes total sense as a magnet is used to complete the switch during calibration, as it is pretty hard to locate a tool while driving (at each wheel) to verify the operation/codes of said wheel sensor. So, in totality, the sensors only transmit when rotating, and the TPMS receiver only holds/displays past/current or a malfunction to the warning lamp.

 

Just go let the air out of one of your tires and then check it for a TPMS indicator.. should remove all doubts..

And here's another tidbit.. TPMS indication with colder weather.. WHILE PARKED adding about 4 psi to each tire the indicator went off..

 

GG is correct about the centrifugal force switching on the transmitter according to the Service Manual.

OPERATION
Each tire pressure sensor/transmitter serves three functions:
² It is used as a valve stem to inflate and deflate the tire.
² It periodically measures tire pressure. (Approximately every 30 seconds.)
² It transmits the tire pressure value to the low tire pressure warning module in the vehicle. (Approximatelyevery 60 seconds or if tire pressure changes by one psi or more between transmissions.)
The system operates by monitoring a radio frequency transmission from the sensor/transmitters located in each
wheel. When the vehicle reaches a speed of approximately 32 km/h (20 mph), centrifugal force created by the rotating wheels closes a roll switch inside each sensor/transmitter, powering up the circuitry.
The sensor/transmitters will only send out information when vehicle speed is above 32 km/h (20 mph). To facilitatetransmitting the radio signal to the TPM module, the valve stem acts as the antenna for the tire pressure sensor/transmitter. When the TPM module senses that pressure is below one of two calibrated thresholds, (low pressure orcritical pressure) the TPM system will set a diagnostic trouble code and indirectly operate the “Low Tire” pressureindicator lamp and the chime tone through the body control module (BCM).
The tire pressure sensor/transmitter is powered by an internal battery. The battery is not replaceable separately. In
the event of battery failure, the entire tire pressure sensor/transmitter at that wheel will require replacement. To extend the life of the battery, the sensor/transmitter is not activated until the vehicle reaches a speed of approximately32 km/h (20 mph) as stated earlier.
Each tire pressure sensor/transmitter has a unique identity code. This will allow the TPM system to indicate to a
technician, through diagnostic trouble codes in the module, which tire of the vehicle has lost air pressure. This code
is also used to identify to a technician which pressure sensor/transmitter has set a diagnostic trouble code. For this
reason, if a tire pressure sensor/transmitter needs to be replaced, the new sensor/transmitter must be programmed
to have its identity code recognized by the receiver.

 

I did this when I first bought the car (to test my first car with a TPMS) and the light did not light. I was going to take it back to the dealer to fix the system until I read the owners manual part about the wheel needing to be turning. I then lowered each wheel and the light cam on (after the lamp reset each time and so on) and thats why I knew about the 20mph thing I re-read last day or so. When I first got my 08 manual set, I was glancing through it (reading it) and remembered the exercise above, and read about the sensors. It just took me a long time to find this reference because I was looking for a TPMS section when it was in the 'wheels' section

What 180 says! Stepping away from keyboard has its disadvantages, especially when coffee deprived and while composing!

 

So if I am reading the service manual correctly and with what others have said here, the light should not have come on while in storage. Not until I drive the car over 20 MPH, which I would never have done without checking tire pressure before leaving the driveway anyhoo.

Important to note, my wife's Sebring TPMS will activate a low tire warning without moving first. More than once I have started her Sebring and be greeted with one or more tires in alarm mode. Also noteworthy is the lights would not go out until we drove the car. This system has individual warnings for each tire and also indicated the pressure on the dash. Much more fancy system than we have on our Xfires so I am sure I am comparing apples to oranges here.

This then would seem to indicate I have other issues. Specifically a Low or dead battery in one or more sensors maybe?? Would that manifest itself while in storage or would that need the 20 MPH rotation to light the warning?

Oh well, makes for good conversation on a snowy day anyhoo. I will pump up all tires to 32, drive the car like hell and see what happens come April. Light stays on after that I pull pin #2 and relocate it to space #6 on the connector. Problem solved.

 

"it's on the internet so it has to be true"

Guess I'm the only one then that has parked their car at night and the next morning had an indicator light.. @ 0 mph...

 

Here's a true quandary :
I KNOW my TPMS sensor and light works, because with the onset of cold weather here, it was on, I checked the pressure and found all 4 below 25 #'s.
After inflating to 33 rear, 32 front, the light went out.

I recently acquired a complete set of 7 spoke wheels and tires, and being the curious George that I am, I decided to try 18's all around.
I put them on the rear and drove probably 30 or so miles testing it out, including several full stop accelerations to 60.

THE TPMS LIGHT NEVER CAME ON !!!

Now, I askya, how in heck did the computer NOT turn the light on ?

( BTW, 18's on the rear looked awful, I put the 19's back on )

 

You shouldn't have put the 19" wheels in the back and passenger seat when testing?