I have been looking at a TPMS (tire pressure)warning for a while. I thought it was related to my spare tire. Checked all of the pressures...33 front and 39 rear. Looking at the tires, they have a slight bulge at the bottom, so I don’t believe my gauge is that far off.
However, the GAP IIDTOOL shows 48 plus PSI. I watched the pressures change as I drove and the tires warmed up a little. I seem to recall getting this warning after airing down to about 15 PSI and wonder if the calibrations have gotten screwed up.
Can’t seem to find anything about calibrating them. My wife’s BMW has a calibration function in the iDrive menus.
I reflashed the Body control ECU. While I didn’t drive it since, the warning light is still on.

Any thoughts or suggestions?

 

Have you confirmed the gauge you are using to check the tires is correct?

 

Curious about this as well.

For whatever reason, my IID Tool has never given me an accurate TPMS reading.
I can be at 20psi or 40psi all around, and my IID just shows values fluctuating between 45-58psi.
At the same time, my low-pressure warning seems to be working fine, and kicks in around 25psi I think.

 

I bought a digital Air inftlation gun because so many people were having TPMS issues based on improper gauge readings. Works great and records PSI to the .00.

 

To be clear, the error you are seeing is "check tire pressure" or is it "TPMS system fault"? (It drives me nuts that it does not actually say which tire to check.)

 

It's the Check Tire Pressure message and the Orange tire icon.
I have a digital gauge on my air tank that I used to fill and a cheap spring loaded stubby that I keep in the glove box. I'll swing by a tire shop and ask them to check the pressures and compare their value to my analog gauge.
I could see 5-10%% variance, but that's almost 50%.
The ride is fine, at least not noticeably stiffer.
As far as calibration, I assume, if anything can be calibrated, it's the ECU. I don't know if the sensors send a pressure or some value that is then converted to PSI.


Thanks for all of the comments above. ndh_cinema: interesting that you believe the IID is inaccurate....I'll reply with my findings. Analog vs Digital vs IID vs Tire shop for reference.

 

I lowered the spare and looked for the TPMS antenna/receiver loop. Didn't see one. Should I have one?
Did not check the pressure of it while lowered. Could be the issue, I guess.

 

When I got home, I checked three gauges against each other and recorded the “Live Values” from the IIDTOOL.
Red and chrome are the two analog gauges and Dig is my digital air chuck for filling. It was too late when I arrived at the shop. They were a little surprised by my numbers. We’ll check batteries in the sensors and the reading their tool shows tomorrow.

LF
RED 31
CHROME 31
DIG 31.6
IID 45.3

RF
RED 34
CHROME 34
DIG 34.7
IID 47.7

LR
RED 34
CHROME 33
DIG 33.9
IID 50.5

RR
RED 36
CHROME 36
DIG 36.7
IID 46.7

 

Autel makes a TPMS tool that reads psi directly from the sensor. We have one if you want to swing by Huntington Beach.

 

I noticed the same thing. IID tool values seem way off (and mine are the same, always between 45-50psi). I would just ignore them.

If it is the spare, it will tell you specifically it is the spare. If it is one of the other tires, it just says check tires, so it is likely one of the ones you are riding on.

Not sure why it is triggering the light if the pressures are OK, but you may want to try bumping the one at 31psi up a bit just to be safe. Otherwise it could be you have an issue with a sensor.