Tire Pressure Sensing "Faulty Warning Light"

[fasteddy]

We are being one of the biggest wheel distributor for smart in North America. There has been a few occasion the customer complaint of the tire pressure warning light come ON for no apparent reason. That's include our own demo car. We had investigate into this issue extensively and recently had found the cause. This is for those who have the warning light ON but all tire pressure seems fine.

Actually this is mentioned in the owner's manual; but they word it in a way that most people could not understand.

There are two device the gives the signal to the computer in order for it to calculate and determine if you have having a faulty tire pressure. Hence turn ON the warning light. One is the tire pressure sensor itself. If it is not there, the warning light will come ON no matter what. The second device that gives information to the (SAM) computer is your wheel speed sensor. The speed of your wheel relates to the overall circumference or diameter of your tire. And this sensor is very sensitive. It is recommended to have your stock tires to be inflated to 36psi in order to have the correct diameter or speed for the computer to think the tire is not flat.

As a smart car owner. We all know that the car will ride very rough at this pressure. On certain after market wheels/tires combination I had try to lower it to as much as 32psi without having the light to come ON. Obviously tread depth will come into play as well as much as ambient temperature. When cold, tire pressure shrinks.

Hope this information helps. Feel free to input more information from your experience here.

[dancote]

I've found that 36 psi all around provides a harsh ride so I set mine to the factory recommended settings. To turn off the warning light, press and hold the sensor button in for several seconds. This resets the indicator light.

Regards,

Dan

[fasteddy]

Hi Dan,

So what pressure do you use?

[Bumble Bee]

Tire preasure sould be balance to 4 tire for even calculation of tooth gear located at cv joint if it is uneven counts that's the time you got the idiot light saying you got flat tire co'z flat tire causes uneven count on the tooth...

[fasteddy]

But the light will comes on if you have a balance pressure all around at a comfort ride pressure say 28psi.

[Bumble Bee]

Teddy, if the tire presure is 28....... then run the car to 35 miles per hour then push the tire sensor untill reset then let me know  this issue is basically the same with mini cooper they have the same SAM

[fasteddy]

Did you actually practice this on a '08 smart?

I know your theory which also work on the B-Class just fine. But many of my clients, including our demo smart, along with my friends at Mercedes could not get it to recognize at pressure under 30 psi on worn stock tires. I did, however, had the pressure at around 29 psi and was able to recognize the system when the stock tires were new.

Now saying that. Not all '08 smart have the light come on with pressure under 36 psi. Only the one's that have this repetitive problem and pump up the pressure evenly and it goes away.

[Bumble Bee]

Ok... if that so .... did you remove the tire on the nosle were you put the tire pressure there is a sensor that identify the presure of the tire that transmit tto the sam.,,,,, then you need to replace this with set presure 28psi this is true wit Nissan 300z's i'll check this were you can get this pressure sensor eqpt.

[Bumble Bee]

Here is the website that gives you the info... maybe you need to replace the sensor to a lower preasure.

http://www.aa1car.com/library/tire_monitors.htm

[fasteddy]

Ok... if that so .... did you remove the tire on the nosle were you put the tire pressure there is a sensor that identify the presure of the tire that transmit tto the sam.,,,,, then you need to replace this with set presure 28psi this is true wit Nissan 300z's i'll check this were you can get this pressure sensor eqpt.

I don't understand what you are trying to say here.

[fasteddy]

Here is the website that gives you the info... maybe you need to replace the sensor to a lower preasure.

http://www.aa1car.com/library/tire_monitors.htm

So, you did not actually practice this on a 2008 smart. The information you provide seems to be in comparing with other cars and/or parts manufacture; but not dedicated to smart in specific.

Are you 100% certain that other car manufacturer you are comparing with utilise 100% same system (software, hardware, and settings) as 2008 smart?

[Bumble Bee]

Ok.... let me do this, I'll break my car one of tire today and let you know i have plan to replace my tire in the front with the same as the rear one's if I found out there is a sensor in the air nosole in the tire i'll let you know how to set this most comon problem in tire repair is the air sensor at the tire and they replace this.... IF there is none therefor this is a tooth grove sensor integrated to the untilock breaks and that would be the SAM issue.

I drove one of the car of smartmadness in Long Beach and first i have observe is the tire sensor is on..due to the fact that they upgrade the tire to a lower profile.

I work on rail sytem basically our train work on tooth sensor breaking in proper grip and identify flat wheels this is basically same in the car but again they use 2 types....air sensor or tooth sensor.

[Bumble Bee]

Fasteddy,
Here are your answers to the question.... If you remove the OEM tire and replace with upgrade you should install the old sensor back to the tire with out this there will be tire sensor at the dash will lit... Ok. If you need to deflate the tire in certain pressure i.e. 28 psi you need to replace the sensor set to 25psi the factory are set to 30 psi and if drop to 3 psi will send alarm to the SAM?

Maybe this will help.