Tyre pressure monitor

[marinaman]

Evening all
Could someone explain this system, i had the red light come on today, went to the code reader and cleared codes but nothing shown,  when it scanned for tyre pressure module  it says, nothing found, along with a lot of other modules.
So, is it connected to new factory tyres. i dont have any run flats on as far as i know, so i found the reset procedure in the handbook,  i did that , the light turned green then went out, i ran the car a few miles and light seems to be out now.
Just like an explanation and why it lights up red for no reason
Thanks

[henrym3]

I know it sounds Like a silly question but have you checked the tyre pressures?

[RickUK]

I had the same red tyre pressure light thingy come on in the 1st week that i bought the X5,so dropped the speed down till i got to the nearest garage,and low and behold the tyre pressure on one of the rear tyres was infact down by a massive margin.Of course blew it up and then hoped it was just nothing wrong.

Reset the the low tyre pressure sensor per handbook,but again next day the same tyre was down again and yes it was a puncture,the rear tyres had only been renewed 2 weeks before it bought 'Big Blue' but the tyre place said that it was able to repair the tyre and no long damage had happened and they only charged me £15 to repair it.

Must admit i have not checked any of the tyres for over a month,everything seems all right,but must admit can get lazy about checking pressures regular these days 

[marinaman]

Yes  checked all pressures, just wondered how the system actually monitors the pressures and if you had to have run flat tyres fitted, is there some sort of sensor somewhere attached to the wheel or inside in whcih case maybe the system works on any type of tyre, but as my scanner said couldnt find a tyre pressure module i presumed i didnt have it fitted till it lit up.

[grumpywurzel]

Mine tends to throw a hissy fit every now and again, check the pressures and 9/10 times they are fine. X5Sport will know for sure how it works

[Greydog]

I believe the system measures rolling radius of the tyres, deflated= smaller radius and triggers the warning.
Then again I am an old bloke and could have imagined reading that.

[Horizon]

[quote="Greydog"]
I believe the system measures rolling radius of the tyres, deflated= smaller radius and triggers the warning.
Then again I am an old bloke and could have imagined reading that.
[/quote]
The system works via the traction control system / wheel sensors. When you reset the system, by pressing and holding the dash button until it goes amber, then it monitors how the wheels rotate and distance covered over a set time/ distance and saves this info.
When the rolling circumference changes due to the tyre deflating it flags up the red light.
So if you reset the system with the incorrect pressures it takes that as the norm. It doesn't monitor pressure but rolling circumference. So always reset after the correct pressure is put in to the tyres.

[marinaman]

Thanks for that ,  learn something new every day on here

[RickUK]

Wow,i was not aware that is how it is done,very simple but very effective.

[X5Sport]

....and a lot cheaper than when a tyre sensor fails @£120 a pop!  Newer BMWs use sensors.