TPMS (Tire Pressure Monitoring Systems)

[Jeremy airjer W]

TPMS (Tire Pressure Monitoring System) is here to stay. After having a couple years of experience dealing with them I thought I would the basics of how they work. Some of this may bore you and some may surprise you but in the end I hope you find it at least a little informative.

To start there are currently 2 different ways that auto manufacturers use to monitor tire pressure. One is an indirect TPMS (Tire Pressure Monitoring System) and the other is the more advanced direct TPMS (Tire Pressure Monitoring System).

Indirect low tire monitoring systems started in the early 90’s and a few manufactures had some version of it by the mid to late 90’s. In concept it is a very simple system. It uses the Current ABS system to monitor tire speed not tire pressure. It uses the principle of a bigger properly inflated tire will turn slower than a smaller under inflated tire. It does have some drawbacks. If both tires are low on one axle or all four tires are low, an indirect TPMS system may not alert you to the low tires. My experience with these has showed numerous times where all four tires will be around 20 – 22 psi (This is the typical tire pressure as the temps drop from the normal temps of summer 70-80 degrees to the cooler temps of winter), with no low tire warning. What does this mean for you? Checking tire pressure on a regular basis especially as the seasons change from hot to cold and back again is just as important on vehicles equipped with these monitoring systems as vehicles equipped without.

Direct Tire Pressure Monitoring Systems (TPMS) on the other hand use individual tire pressure monitors that are mounted in each wheel and sometimes the spare. Each sensor has a battery, a pressure sensor, a microprocessor and an RF transmitter. Pressure data is sent to a receiver located in the vehicle. If the receiver sees a problem it will turn on the low tire light or message. These sensors can be attached to the inside of the wheel with a steel band or they can be mounted as part of the valve stem, GM’s new sensors actually look like a rubber valve stem. Because each wheel has its own pressure sensor this type of system is more accurate and reliable that the indirect system. The sensors are typically accurate to within a couple of PSI and have a life expectancy of 7 to 10 years.

Typical Direct TPMS Sensor

Band Style Direct TPMS Sensor

GM's New Rubber Valve Stem Looking Direct TPMS Sensor

A basic direct TPMS system will alert you to a low tire (about 25% low or 6 to 8 lbs on average) by turning on a low tire light. A more advanced direct TPMS system will not only alert you to a low tire but can display individual tire pressures.

Universal Low Tire Symbol

Typical Individual Pressure Display

There are two different ways that a direct TPMS can learn its tire position, active and passive. Active systems will automatically locate the position of each wheel. It does this by having a receiver near each wheel so that it can pick-up each wheels individual signal. Passive systems require the position of each wheel to be manually relearned after the wheel positions have changed. There are many different ways this can be done, every manufacturer is different, and even the different models in a manufacturers line can be different. Most manufacturers use a passive system. If your vehicle displays tire pressure for each wheel then it would be worthwhile to have there positions relearned after rotations and replacement of the tires. Why is this important? Lets say your low tire light comes on and you notice that the tire pressure display says that your right front tire is at 25psi. When you check the right front tire it’s at 32psi. This may be because you recently had new tires put on and the wheel that was on the right front is now on the left rear. Since a relearn was not done the vehicle still thinks that wheel is on the right front.

A couple of things to consider.

1. It’s always important to check tire pressure on a regular basis especially with the season changes we have.

2. Keep those valve caps on your TPMS sensors. They are not cheap, keeping the dust, salt, moister out of the valve stems will help prolong there life.

3.Do not use fix-a-flat products if your vehicle is equipped with a direct TPMS system!

4.Aftermarket TPMS kits are available to retrofit older vehicles as well as campers and trailers. They are relatively cost effective with systems starting around $300.

[jwhjr]

Is the relearn something that can be done by a do-it-yourselfer? What's needed?

[DTro]

Well I hope these will be a little "smarter" than the rotational calculation type. They just don't work well enough. Rotate the tires, light comes on, but yet all tires are low, no light comes on.

Frustrating....

I do forsee people becoming anal about a pound or two of pressure though, when the numbers are staring you in the face

[Jeremy airjer W]

 Originally Posted By: jwhjr

Is the relearn something that can be done by a do-it-yourselfer? What's needed?

It all depends on the make and model. Some can relearn through a process of inflating the tires to a certain pressure and then deflating, after the relearn procedure has been activated. Others require a special magnet. We have a basic tool that "activates the sensors". The more advanced tools will read the serial number of each individual sensor as well as give the pressure it is sensing.

If your curious you can post Year Make and Model and I will get the info for you. You can also visit you local library. Most will have alldata (automotive information source) which is offered at no charge.

 Quote:

I do forsee people becoming anal about a pound or two of pressure though

It hasn't been to bad but there have been a few!

[jwhjr]

Thanks airjer. I don't have a vehicle with it right now (04 Silverado and 99 Suburban), but I'm sure my next one will so I was just wondering. I do have a friend with a 08 Malibu that has it though...

[Shack]

I know aftermarket tire shops are getting on the page when comes to tire pressure monitoring systems, but if you have a monitoring system on your veh., it is a good idea to let the shop know before they replace your tires. These sensors snap like twigs if the tire is not removed correctly. Again I think most shops will know on their own, but it never hurts to tell them.

Also on some makes and models, the spare tire is monitored in this system. If you check all your tires and the minder is still on, check you’re spare.

Great read Airjer .

[BobT]

One thing I learned this year is that low pressure along with reduced mileage also increases the risk of losing air past the bead with our aluminum rims. I check mine about once a month but the last cold snap resulted in enough drop in pressure (24psi) that I had a tire go flat on the highway. Took it in, they found nothing wrong, resealed the bead and I put it back on. The shop told me that mine was one of five others he had that day. I never experienced that before with steal rims.

Bob

[Scott K]

Aluminum wheels corode at the bead, with low pressure there is less pressure pushing the tire against the wheel. This applies to steel wheels also. Its just with the corrosion on the alum wheel it tends to leak more then steel.

Either that or the shop had a rookie repairing tires that day, and didnt know what he was doing!

[Scott K]

TPMS as Airjer stated will be on every vehicle line soon! For the customers view point they are great, lets them know if a tire is low. For the shops view point, they are a pain in the ***! If every manufacturer used the same procedure, it wouldnt be bad. But as of right now, it is different from car to car, year to year, manufacturer to manufacturer. Just a simple tire rotate, you can spend an extra half hour reading on how to reset the TPMS. Most cars have the info in the owners manual, but for some reason, alot of customers dont have the owners manual in their car! Some foriegn vehicles need a tool to reset it, and alot of shops wont have these tools, and some just dont even have the option, so you spend the half hour trying to reset it, and find out, it doesnt even have it!

So if for some reason your TPMS light comes on after you had your tires rotated, please be curtious to the mechanics, or service writer!

[fishin58]

We have had great success with nitrogen and the tpms lights staing off. In November we started putting in nitrogen into our new and certified vehicles. I cannot think of one vehicle coming back with a light on. I put it into my Vehicle witout tpms and I have checked the pressure and it hasnt went down at all this winter. With the nitogen it is a bigger molecule, which basically has a harder time escaping the beed on the tire. www . getnitrogen dot com should give you some good info

[Shack]

Also it helps with leaking cold time alum. rims.

[Scott K]

Our shop didnt want to buy the nitrogen setup. Sounds like it works good. How well does it work in low pressure tires such as atv tires?

[Shack]

Just as well.

It cut down the tire minder light issues with Chrysler by 3/4 the first winter we had the machine.

[fishermn]

Airjer, Excellent post! I knew about the older style systems that looked at wheel speed differential, but I was wondering how the newer vehicles were doing this and actually reporting pressure of each tire.

One stupid question though... Is there a real need for this or is it just a convenience. I'm a firm believer in keeping things simple. Oh and just how expendsive are these units if one were to get busted during a tire replacement?

[Shack]

The government says there is a need for them “legally” in new models. This all came about from the Ford/Firestone recall.

As far as replacing a factory one, it would depend on the make and model for price. On most domestics, it would be around $20-$40. Some higher end models and imports I would guess $60-$100. Most times the shop would be held responsible for a breakage, but you never know. Now-a-days things may be better, but find the one to fit your car was a bigger issue. They had to be order in and you would have to come back, even if there was no charge.

[Jeremy airjer W]

 Originally Posted By: fishermn

One stupid question though... Is there a real need for this or is it just a convenience. I'm a firm believer in keeping things simple.

IMO, yes. If you came by the shop from late fall to early winter and even now you would be surprised at the number of vehicles with low tires and even more amazed at the number of pressures below 18psi. On a regular basis throughout the winter I will see front wheel drive cars with 50 - 60 psi in the fronts and less than 15 psi in the rear.

as far as cost, if you can get one replaced at a shop for around $100 parts and labor you'd be in the ball park.

The problems we have seen this winter are leaking valve cores because of loose caps that allow moister into the stem wich freezes and open up the valve. Broken stems after running through a frozen snow bank. Loose retainers, a quick retorque (yes there is a torque spec on these!) of the retainer and they are fine. I have run into a few that where dead. They where within there manufacturer warranty so the customers brought them do the dealer for service.

[Shack]

My post kind of sounded negative towards them, but I sure did not mean it that way. I think for some, the tire minders can mean life or death for some people. They are needed and are a great tool for notifying people of a major issue with their car/van/truck.

[Jeremy airjer W]

Here's a funny story. The Low Tire Light came on in my Tundra last fall, as I expected it to. Checked all the tires and the right rear and spare where low. Reset the light and a week later it came back on. The temps had dropped so no big deal. Checked the tires and they where all a little low, R.R. more than the rest (no connection made yet on my part) about a week later the light comes on again the temps had dropped again and I'm thinking to myself this never happened last year. Then the connection was made. Sure enough the R.R. had a nail in it and the leak was slow enough that it would take about a week to trigger the Low Tire Light. Here I was becoming frustrated with it and it was doing exactly what it was supposed to be doing, letting me know there was a problem!

[Mlaker3]

I own a 2006 Toyota Tacoma, tire sensor worked so-so when I had Bridgestone tires on. The low tire pressure sensor will not turn off with the Goodyears I have on now. PIA/POS when they don't work and the light is always on. Now I just ignore it as I have 35+ psi and the indicator light WILL NOT turn off.

[Jeremy airjer W]

If it is not blinking than either the spare is low (very possible that the spare has a sensor), They are over inflated (they can warn you of over inflation), one of the sensors is reading incorrectly.

If its on steady it is likely an inflation issue. If it blinks there is a problem with the system. It might be worth giving Toyota a call and just running your scenario by them and see if they have an answer!

[Dale Rueber]

On my 2005 Tundra there is a reset button under the base of the steering column that I have to press after inflating the tires to the same pressure to get the light to go out. Maybe the Tacoma has something similar. In the manual it is labeled as "Tire pressure warning system reset switch".

[Jeremy airjer W]

Funfish made a good point to check the owners manuel for information on resetting the light. There are many different ways manufacturers have come up. Some vehicles have a button, some have a series of steps, Some automatically reset themselves after X amount of miles at over X speed.

[Mlaker3]

Thanks for the effort but I have spent too much time already with it, the tire dealer is sick of it as well. Not worth it for an one-who-thinks-I-am-silly light. It's part of my "I'm not happy with my Toyota" rant.

[Scott K]

Another thing that could have happened, is when they put the new tires on they damaged the sensors.

[Jeremy airjer W]

 Originally Posted By: Mlaker3

Thanks for the effort but I have spent too much time already with it, the tire dealer is sick of it as well.

Not to pick on the tire dealer but it is entirely possible that they do not have the experience, equipment, or proper information (or a combination of all of these). This is a relatively new technology and the learning curves and information resources take a while to get to the independent shops. At this point in our shop we have basic equipment to deal with these. Anything other than replacing or repairing a physically broken sensor we typically recommend our customers see the dealer.