[id5]

It seems that my problem has nothing to do with the AWD system but I thought that I would post a copy of the post from the thread in the V40 section just in case anyone comes looking.

Originally Posted by SwissXC90

A 50% drop to trigger the TPMS is about right

TPMS that uses in-tyre radio transmitters are very accurate and can trigger at just a few PSI drop, as they directly measure the tyre pressure. they are not subject to distance, speed, or road geometry.

TPMS that uses wheel rotation sensors, such as yours, need a much MUCH larger drop in tyre pressure to trigger the TPMS
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Thanks for your input SwissXC90.

I am still waiting for a response from Volvo so I though that I would take a break from work and spend a while digging into the subject to see what I can find out, so here goes. Volvo may call them TPMS and TPM, but they are really Direct TPMS (dTPMS) and Indirect TPMS (iTPMS). I have always known that my V40 has TPM (iTPMS) and was told that it is triggered by the ESC(ABS) wheel sensor and It is based on the earlier versions of iTPMS, here is how that works. To get type approval it must be able to notice the pressure drop in one wheel before it loses 20% of pressure or 1.5bar or any four tyres after 60 minutes.

But there are flaws in the system, and it cannot notice a slow pressure drop in both wheels on the same axle, has problems with the type of road, tyre construction, weather, etc or because the software tries to tune out false alerts, just plain doesn’t work.

Moral of the story, check your tyre pressures often and don’t bother trying to fix TPM.