low tire pressure warning

[GPSnV1]

Originally Posted by motordavid

I have real time/real psi readout on my '02 Vette but I've
never seen that severe of a psi drop, induced by temp change.

I do see a few psi fall off from our occasional 75+ degree autumn
days vs our less than 30 deg nights, but I only see a few psi drop
even under those conditions. I also "gain" a lb or so, descending from
5,000 ft elev. to the "flats" down below, due to less atmospheric pressure
at this elev., I think.

Either its an edgy "system" or the tires were borderline in psi, or
it's another BMW low tech gizmo "monitoring" deal, imo.
GL,mD

Are the RFTs a factor in addition to the minimal tire monitor system?

[JCL]

Originally Posted by GPSnV1

Are the RFTs a factor in addition to the minimal tire monitor system?

I don't believe they are. I had RFTs on my Z4, with the basic BMW ABS sensor (wheel speed) tire pressure system, and the only time the alarm went off was with a low tire (repaired each time).

With actual pressure sensors, you get an alarm with temperature drop if the tires were borderline inflated to start. With the sensors that just measured rolling diameter (from the ABS sensors) all the tires went lower at similar rates with a temperature drop, and the alarm therefore didn't go off. The alarm was based on a difference in rolling velocity between tires. That is likely what was happening with your last X5, all the tires being low wouldn't cause an alarm.

Yes, it can be a nuisance, but you will also get better mileage, better handling, and better tire life with the correct pressures that this system is prompting you to achieve.

[motordavid]

Originally Posted by GPSnV1

Are the RFTs a factor in addition to the minimal tire monitor system?

I don't think so, either. On my Vette, (not apples to apples vs your
E70, I realize), I actually got more consistent real time psi readouts
from my orig set of RFTs...and, less variation due to ambient temp,
warm vs "hot tire" temps, etc., vs the non-RFTs I finally installed
as replacements. Strictly Fwiw.
GL, mD

[Nutinup]

how about re-setting the TPMS and go from there.... ~

[Penguin]

> I never experienced anything like this with my '04 4.4i and was completely caught off guard.

I believe the older models had the inferior indirect system and therefore will not tel you if all the tire pressures drop equally, e.g., if all four tire drop to 15 psi, the old system would not warn you.

[GPSnV1]

Originally Posted by Nutinup

how about re-setting the TPMS and go from there.... ~

If you are going back to the OP, in the earliest stage I tried to do this but it would not reset. I now better understand what was going on and what to do (about yesterday's problem) but at the time thought there was a nail in one of the tires so just accepted the logic of the computer at face value.

[mtech8]

Okay. Just experienced this myself.

The weather here suddenly dropped about 20-30 degrees. In the morning, when I started up the car, the low pressure warning light came on. At first, I thought I had a flat. After inspection of the tires (looked alright) and then looking closer at the iDrive's screen (all tires where displayed as yellow, not just one in a flat tire scenario), I proceeded to measure the actual tire pressure.

The fronts were 27.5 while the back 30.5.

What are the suppose to be?

And after properly inflating them, I should just select the reset (TPM) on the iDrive, right?

[JCL]

Originally Posted by mtech8

The fronts were 27.5 while the back 30.5.

What are the suppose to be?

And after properly inflating them, I should just select the reset (TPM) on the iDrive, right?

The correct pressures are shown on the label on your driver's door jamb.

Yes, after setting the pressure you reset the monitoring with the iDrive. Follow the instructions on the screen.

[PasPar2]

same thing happened to me. false alert on rear tires. checked pressure (spot on 35psi) and reset the system.

[SpeedTriple]

How difficult would it be to have the TPMS give a quantitative measurement of tire pressure? With the current system, it's difficult to tell from the alert whether it's just a low pressure situation or an actual flat. It's not that big of a deal normally, but when you're driving on an icy, windy road with wife, kid, and newborn, the TPMS alert is not only perplexing but stressful. As with the rear view camera, the TPMS goes into the half-assed department of not going all the way. Grrr.