# Low pressure tire sensor - shop scam?



## Mike G (Mar 10, 2006)

Had my first flat on my '05 Frontier the other day. After changing the tire the low pressure warning light remained on. I finally figured out that the spare - full sized with new rim - does NOT include the sensor.

Bottom line: move the patched tire to the spare rim, or have Nissan install another sensor! What a scam.


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## neicedover1982 (Jan 27, 2006)

I never had to change to put on my spare (knock on wood), but that is a really stupid thing. Since its a full size, its not like if you get a flat and put it on, you need to get the other fixed right away, you can drive a while on it. You would think since of this, they would have the sensor on the spare.


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## smokeydadog (May 30, 2005)

I thought I read that the sensor was on the valve stem cap. Have you tried swapping those? I could be totally wrong on this...


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## scuba91ta (Aug 19, 2005)

the sensor is the valve stem - not easily changed and you need to take the tire off to do it - also, it is known that there is not sensor int he spare... 

I think the system only supports 4 sensors anyways... 

Also, why not drive on the patched tire??? not really seeing how it is a scam...


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## smokeydadog (May 30, 2005)

So the metal valve stem caps are just for looks? That's good to know; I've been wanting to change those out since I got the truck.


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## articulate (Jan 26, 2006)

Mike G said:


> Had my first flat on my '05 Frontier the other day. After changing the tire the low pressure warning light remained on. I finally figured out that the spare - full sized with new rim - does NOT include the sensor.
> 
> Bottom line: move the patched tire to the spare rim, or have Nissan install another sensor! What a scam.


I wonder which wheels you have. I recall reading in the manual that Nissan does not recommend a 5-wheel rotation; I had no idea why. But I got a flat also and noticed that while the 5th wheel is the same size, it does not match the other 4 (it's steel). I figured that might be why. 

Sensor or not, the wheel doesn't match anyway - unless yours do. 

Is there any problem with driving on the patched tire? I suppose it could be compromised because of the patch...


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## MrFancypants (Nov 18, 2005)

articulate said:


> Sensor or not, the wheel doesn't match anyway - unless yours do.


Sounds like you got the steel spare? Nissan switched to a matching spare midway through the 2005 model year. Probably around when they aluminum driveshaft and chrome accents came out.

Not sure if my matching alloy spare has a sensor in it though.


- Greg -


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## articulate (Jan 26, 2006)

Greg, yes my spare is steel.

Methinks again.....
If they do not recommend a 5-wheel tire rotation, the reason could be because sensor is not on all 5 wheels.

Perhaps not a scam, but just an area for improvement on the next go-round.

Cheers,
Mark


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## scuba91ta (Aug 19, 2005)

yeah - no chrome stuff here - but i did get the alum shaft, and the mathcing nismo spare wheel


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## Centurion (Sep 5, 2002)

Oh great. I have the full-size spare w/'matching alloy and I was looking forward to a 5-tire rotation. I guess I won't be doing that, but I don't know why it can't read the sensor in the spare's cradle (put there after the rotation of course given that we have only a total of 4 sensors).


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## MrFancypants (Nov 18, 2005)

Well it's not like the truck wont drive without four operating sensors. You could do a 5 wheel rotation and just ignore or defeat the TPMS. Although, if you have 4x4 the electronic disengagement might complain on you.


- Greg -


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## Franko Manini (Nov 22, 2005)

scuba91ta said:


> yeah - no chrome stuff here - but i did get the alum shaft, and the mathcing nismo spare wheel


You're in exactly the same place I am. Matching alloy NISMO spare, Al driveshaft, and no chrome. Build date on my track is Feb 05.

I read somewhere on this forum that one guys was successful in getting NISSAN to upgrade his mirrors and door handles to chrome. I wish.


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## Franko Manini (Nov 22, 2005)

Centurion said:


> Oh great. I have the full-size spare w/'matching alloy and I was looking forward to a 5-tire rotation. I guess I won't be doing that, but I don't know why it can't read the sensor in the spare's cradle (put there after the rotation of course given that we have only a total of 4 sensors).


I think it would be great idea to monitor the pressure in the spare as well. Hmmm... modification?

I used to be a tow truck driver and you would not believe how many of my calls could have been eliminated if the spare wasn't flat!


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## Mike G (Mar 10, 2006)

*a couple more thoughts*

Lots of bad info around this. A couple trueisms before I drop it.

1. The sensor is not in the valve stem or cap. There are color caps systems but they are junk. Might as well stick a mood ring on there.

2. On the '05 Frontier the sensor is mounted in the wheel and is (believe it or not) based on the rate of rotation of the tire. As a tire deflates, its diameter decreases and affects the rate of rotation the sensor "counts" this and sends it to the computer. This sensor assembly must be mounted into spare CHA-CHING. And the spare tire/rim/wheel must match exactly CHA-CHING if you want to have a 5-tire rotation. Toyotas have a simple pressure-based system that you can reset when you change tires.

3. And for the guy who doesn't mind driving around on a patched tire when he could be using a perfectly good full-sized spare, what can I say?


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## azrocketman (Oct 5, 2005)

"2. On the '05 Frontier the sensor is mounted in the wheel and is (believe it or not) based on the rate of rotation of the tire. As a tire deflates, its diameter decreases and affects the rate of rotation the sensor "counts" this and sends it to the computer. This sensor assembly must be mounted into spare CHA-CHING. And the spare tire/rim/wheel must match exactly CHA-CHING if you want to have a 5-tire rotation. Toyotas have a simple pressure-based system that you can reset when you change tires."

I'm doubtful as to whether the sensor is actually mounted in the wheel. My knowledge of these systems indicates that the sensor is the same sensor as that used for the ABS system. Since both systems (ABS and low pressure) are measuring wheel rotation it seems logical that the same sensor is used for both. The sensor is probably part of the braking system components. There's been some debate that this is not a "true" low pressure system, but, since it uses existing hardware and only requires computer programming it's a cheaper approach. The use of pressure transducers for each wheel, while a technically better approach, is more expensive. I'd be curious, whether owners who have replaced all four wheels with aftermarket parts have experienced any similar problems.


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## avenger (Oct 7, 2005)

matchine spare, alum drive shaft, chrome accents... hooray for buying in september


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## Reverendbiker (Jan 29, 2005)

azrocketman said:


> "2. On the '05 Frontier the sensor is mounted in the wheel and is (believe it or not) based on the rate of rotation of the tire. As a tire deflates, its diameter decreases and affects the rate of rotation the sensor "counts" this and sends it to the computer. This sensor assembly must be mounted into spare CHA-CHING. And the spare tire/rim/wheel must match exactly CHA-CHING if you want to have a 5-tire rotation. Toyotas have a simple pressure-based system that you can reset when you change tires."
> 
> I'm doubtful as to whether the sensor is actually mounted in the wheel. My knowledge of these systems indicates that the sensor is the same sensor as that used for the ABS system. Since both systems (ABS and low pressure) are measuring wheel rotation it seems logical that the same sensor is used for both. The sensor is probably part of the braking system components. There's been some debate that this is not a "true" low pressure system, but, since it uses existing hardware and only requires computer programming it's a cheaper approach. The use of pressure transducers for each wheel, while a technically better approach, is more expensive. I'd be curious, whether owners who have replaced all four wheels with aftermarket parts have experienced any similar problems.


Nope--Mike was correct. The sensors is attached to the wheel inside the tire. If you ever have to change or repair a tire you might want to alert the tire-shop mechanic to watch for it; it's tucked up against the rim, but if he gets rowdy with the machine he could destroy it.


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## SonsofWisdom (Mar 29, 2004)

That's odd. With Toyota, if the tire pressure system has sensors mounted in the tires, even if the spare is a steelie, the spare has a sensor.


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## brownboy (Jan 24, 2006)

i had to replace my right rear tire yesterday was doing a bit of wheeling and ran over a beer bottle someone threw out on the trail. i put the spare on ( a full size matchinig alloy) drove another 60 or so miles with no tire pressure warning light going off. the production date of my kc nismo 4x4 is nov 04. i bought it oct 05 ~14,000 miles now. is there a possibility that the spare has a sensor for the tpms? i noticed the flat when we took a break for lunch, and the warning light never came on when i started the truck up.


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## Gerald (May 23, 2005)

brownboy,

The spare does not have a sensor. When I had my wheels polished I had to take them one at a time to the polisher so I had them dismounted one at a time using the spare
wheel while the originals were in being balanced.

I kept the spare tire off of the truck by just storing it while the work was being done. There is a sensor in the 4 wheels
on the ground, but the spare does not have a sensor.

The tire shop I used did not have a problem switching the 
sensors over to the spare rim each time.

OkieScot


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## scuba91ta (Aug 19, 2005)

Mike G said:


> Lots of bad info around this. A couple trueisms before I drop it.
> 
> 1. The sensor is not in the valve stem or cap. There are color caps systems but they are junk. Might as well stick a mood ring on there.
> 
> ...


So your saying driving around on a tire with no wear on it is a good thing for the 4wd system? read the owners manual dude... Tires need to be as close as possible to the same size. Secondly, if you have doubts about the reliability of a repair, you should buy a new tire... 

Secondly, Sorry i wasn't clear, the sensor is mounted on the rim beneath where the valve stem is - this is so people can pull a tire off with out damaging the sensor - nobody that knows what they are doing will let the bead breaker slide up on the wheel where the valve stem is. As for the rotational counting system, sounds intresting, i always knew them to be pressure sensors, as i don't see a way for the sensor to be able to distinguish a full turn from another - especially seeing that in 4wd, with the e locker on, all the tires will rotate the same amount, flat or not... if one doesn't have the same diameter, then it will drag.

Another question - does the circumferance really change with loss of air pressure - the circumference in a steel belted radial can't really change much...


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## 05 NISMO 4X4 (Jun 4, 2005)

Brownboy, does your spare have a steel valve stem? If so you may have a sensor in the wheel, if you have a rubber valve stem you don't. I've thought about purchasing an extra sensor just for the reasons stated above, if I get a flat, and have it repaired, I'd probably just leave the spare on the truck and use the repaired tire for the spare (more out of lazyness than anything else). I have a matching wheel on my spare, and if there were a sensor on all five wheels, there's no reason to pull the spare and replace it with the repaired tire again!! As for a difference in the diameter of the spare and a tire that's already on the truck, we're ony talking a couple thousandths of an inch difference due to wear! I'm sure the mechanical tolarances in the driveline have enough slop to compensate for that small a difference (assuming they are all the same size and brand of tire of course!).

My Explorer had a sensor on the spare, and the monitoring system on it could tell which tire was low, I know because the alarm went off one day and it indicated the spare was low, sure enough, I checked and it was at 28 lbs! I wish the Frontier system worked the same...


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## scuba91ta (Aug 19, 2005)

Here's the real deal from a little research... 

According to the article on tire rack, nissan uses Schrader TPMS (tire pressure monitoring system) I call my Nissan dealer, and they confirmed this after talking to a tech.

Info on the Schrader system -

*Title :*
Tire pressure monitor and location identification system and method
*Document:*
United States Patent 6362731

*Abstract:*
A method and system for monitoring and reporting vehicle tire pressure information. The system includes _*tire pressure monitors*_ mounted to the tires of a vehicle. The tire pressure monitors detect tire pressure information from their respective tires and transmit that information to transponders that are fixedly-mounted to the vehicle. Each tire pressure monitor corresponds to a single transponder. When a tire pressure monitor _*transmits tire pressure information*_, the corresponding transponder receives the signal and transmits the tire pressure signal along with a unique transponder identification code to a vehicle central system controller. Based upon the transponder identification code, the central controller associates the tire pressure information with a particular tire location. However, under certain conditions, a transmitted tire pressure signal is received by one or more of the non-corresponding transponders as well as the corresponding transponder. To filter out the stray tire pressure signals, each of the receiving transponders detects the strength of the received tire pressure signal. The system then determines which of the receiving transponders is the corresponding transponder based upon the respective signal strengths.

According to that Document,


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## scuba91ta (Aug 19, 2005)

> we're ony talking a couple thousandths of an inch difference due to wear!


No.... 

Go measure the tread depth on your spare and on one of your corner tires - especially after 10k - approx 1/3 to 1/4 of the avg life for a set of the bfg tires... the wear bars are a full 3/8" deeper than the top of the tread blocks - remember in talking about diamters, subtract another 3/8" for the other side... 

Circumferance is Pie*D - lets take 31" diamter - thats a circumferance of 97.34

Lets do a worn tire - if the difference in tread depth is an 1/8" - total of 1/4" diameter - 30.75 * 3.14 - 96.56 little more than a 3/4" of cicumferance difference - and thats with minimal tread wear... like 10k miles worth... 

Anyways, the difference between new and old in circumferance can be as high as 3 inches! and what more is that is per one rotation... take a mile - 5280ft - tire rotates 170.3 times at full 31" diameter... at the 30.75 diameter, tire needs to rotate 171.7 times to go the same distance... a full turn and a half - thats a lot of bind on a locked system... People who complain about the 4wd being sluggish to disenguage often have this sort of a problem... 

Regardless, they should have put a sensor in the spare... what i would like to know about the system is how does it know where it is on the vehicle if you rotate tires front to back?

I also don't mean to sound assholish - thats not the point, nothing is ever accomplished by outright arguing... Just understand I have a pretty good knowledge of this type of thing, and when i'm wrong i'll admit it, but i'm not wrong too often... infact, you almost had me admiting being wrong


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## MrFancypants (Nov 18, 2005)

scuba91ta said:


> Here's the real deal from a little research...


I found the whole "rotational calculation" thing to be far fetched too. Glad to see it was.

I actually checked the FSM this time and here's what it says:

"A sensor-transmitter integrated with a valve is installed on a wheel, and transmits a detected air pressure signal in the form of a radio wave."

Then I read a little further and found out that the receiver needs to know the transponder's identity. You can only program up to 4 transponders. In other words, adding a transponder to your spare is a waste of money. You would have to recalibrate the brain for the new transponder once you change the tire -- probably more trouble than it's worth since a spare is after all for temporary use.



- Greg -


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## brownboy (Jan 24, 2006)

i just checked the spare i have has a metal valve stem so maybe it does have a tpms sensor in it. I guess if no warning lights are going off i'll keep the spare on there and just get the other tire patched and keep it as a spare. thanks for the imput guys.


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## scuba91ta (Aug 19, 2005)

Greg - The way the patent abstract reads it almost seems as though there is a reciever for each wheel in close proxcimity to each wheel - so it may not be - the sensor may just detect a nearby transponder.


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## MrFancypants (Nov 18, 2005)

scuba91ta said:


> Greg - The way the patent abstract reads it almost seems as though there is a reciever for each wheel in close proxcimity to each wheel - so it may not be - the sensor may just detect a nearby transponder.


True but the FSM goes into detail on how to calibrate the TPMS system, and the procedure is for only 4 tires. Basically you fill each tire to a preset pressure, then put the system in calibration mode and go for a spin. It only lists LF, RF, LR and RR in the table. The preset pressure is how the brain knows which tire is where.


- Greg -


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## scuba91ta (Aug 19, 2005)

hmmm very intresting... i need to get the new adaptor for my scan tool to read the can network so i can see all that stuff


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## Cascabel3 (Aug 12, 2005)

*Tire pressure light on*

When I bought my brandnew 05 Nissan Frontier late last year, she came with 33" BFGoodrich Mud Terrain tires. The reason; it was a display truck. They were going to put stock tites back on but I wanted them. I had a 2" lift and did some cutting on the mudflaps and was good to go. However, from the beginning on; after driving for a minimum of one hour my tire pressure sensor light comes on. Pressure is equal on all tires. I haven't yet brought it to the dealer but wonder if someone else has had this experience. If I turn the engine off, sensor light goes off and after an hour of driving comes back on.


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