I've got a 2005 545, and it uses wheel speed, not air pressure to calculate a tire problem.

This morning on the way to work, I got a "flat tire" warning on the display, but the tires don't appear to be low at all. I don't have a pressure gauge at the office, but after 25 years of driving, I've seen low tires before, and recognize the symptoms. I do not have run-flats, just my Bridgestone Blizzaks fitted.

I am wondering if the snow/slush/ice driving is causing tire slippage and tossing an erroneous flat warning on the screen? The streets in Michigan are a sloppy mess today.

My other cars all have pressure sensors mounted to the rim, so this is my first winter driving with this type of TPMS.

 

I don't know how the speed one works.. I have an 08 which said it has I believe 5psi swing.

 

The Flat Tire Monitor (FTM) works by comparing speeds of all four wheels to one another as recorded when the FTM is initialized. When a tire looses pressure, the diameter of the tire changes and thus it speeds changes from the initialized setting or as compared to the other tire on the same axle. I believe at least a 10psi differential in pressures is required to trigger the FTM. My experience is between a 10 and 20 psi loss of pressure. Works fine for slow leaks, but for larger punctures, it will almost be too late to avoid tire damage.

 

Have a look here:
https://www.google.com/url?sa=t&rct=...82001339,d.cGU

 

Cold weather can have an affect on tire pressures. If its really cold where you live, which is most of the country...it can trigger a low tire.

 

Not if all tires are colder and have lost pressure, since the sytem compares the wheel revs with each other looking for a 10% difference and the chances that only one tire got a lot colder than the others is pretty small..

OP should just try resetting the sytem. I have had this happen after changing over to winter tires - the shop did not reset the tire monitoring system (I didn't ask them too, since I knew that I was going to do that, but I forgot) and I got the flat tire message about 30 kms later.

Salut, Bob P.

 

I had a slow pumcture last year, usually a 7psi or so drop would fire the wirning on the dash, as a rule it could be reset twice and the tyre, while low, was safe to drive on. its pretty sensitive, speciallt at speed like motorway(highway)

 

TWH, your link is broken.

Thanks for the replies. I did check the tires when I got home from the office. All of them were slightly low because of the low temps in Michigan. The left front was about 5lbs lower than the right front.

I reset the system, if it goes off again, I will take it back to the tire shop and get the leak fixed.

 

Then that is what set the alarm off - 5lbs is greater than 10% difference with the right front. If you have reset without adding air to the left front, the system will now think that this difference is normal and if the leak continues the alarm will go off again when another 3lbs pressure are lost. If there is no further loss, then you are still 'stuck' with a 5lbs pressure difference on the front wheels.

I would add air to the right front to equalize with the left front and reset the system and see if you lose pressure again at the left front. 5lbs difference is too great a difference in my opinion for good carhandling and response.

Salut, Bob P.

 

Sorry, I should have been more clear. I added air to the tires, so they were all to spec before I reset the FTM system.