mvvette97

2006 530i. Driving to des moines iowa today to see the dr. and all at once I heard the warning chime and it told me to pull over because of a flat tire. So pulled over in the busy interstate and no flat tire. So went on my way to my dr visit with the red tire warning lit up. Drove home and stopped to buy a tire pressure gauge to check them and they all had about 40 psi in them. Guessing from the heat of the long drive. i lowered them all down to what the door sticker said and went on home. i finally figured out how to reset the tire monitor system and went for a drive for about 10 miles. so far now warning. Any idea what could of caused this? Could too high of pressure of done this? If so I would not of thought it would of said I had a flat Also how the heck does it even know about the tires because it doesn't even have any sensors in the wheels. I know this because I put new tires on last winter and it had just normal valve stems. I assumed it didn't even have any kind of tire monitor system. Very strange

DanielFD

you are thinking of TPMS, you have FTM, it works off of the ABS sensors in the hubs, detects a slower rotating tire to be a flat"er" tire. could be a hiccup in the system, because FTM can only detect a flat or change in pressure if the pressure is different on only one tire because it compares the rotation of the opposite side tire. so if all your tires are all flat or they are all over inflated then it wont throw a warning. Also not recommended to pressure tires when they are hot. the tire pressures on the car and in the manual are cold tire pressures, meaning when the tire is completely cold. driving more then a mile will cause heat buildup inside the tire increasing the pressure. next time you drive your car have them reinflated as close as possible to home, then reset the warning again. you have about 23-25 psi cold temperature air in them at the max if you readjusted while they were hot.

mvvette97

Ok I understand how it works now. Come to think of it one tire was at 45 or so and the rest was at 40 or just under a bit. I wonder if that one tire could of been enough to throw it off?

DanielFD

Thats exactly what it takes, just one tire, anything more and you woulnd't see an error. Thats how it works and why its called FTM or Flat Tire Monitor and not the sensor in the tire system called TPMS or Tire Pressure Monitoring System