[s-cars] tire pressure sensors

[David Giannandrea]

I just ordered the Bentley for the 2008 A4 which should answer some of the
following questions about tire pressure sensors. But this group has so much
more knowledge I need to ask anyway.

I looked into the measurement values and found pressures reported that were
way off from readings taken at the tires. With about 37psi in each tire I
got readings between 1.87 to 2.55 bar. This calculated to 36,29,30,27psi for
the 4 tires, and of course, the tire pressure warning light is on.

Are there batteries in the pressure sensors??

I guess I just replace the ones that are wildly inaccurate. That would be 3
of the 5.

I thought these things were a bit more reliable than that. What's the
wisdom?

David G.