Why does my TPMS keep giving me a warning?

I have a 2009 Jaguar XFR. 12 months ago the tyre pressure warning came up on the dash. I pulled over and checked but the pressures were fine. Since then the fault has repeated frequently, always in motorway type travel conditions. A Jaguar dealer has twice checked the system but no fault found and they are reluctant to start replacing parts if they don't know what they are fixing.

Asked on 25 July 2018 by R A Buckingham

Answered by Honest John
TPMS gets tricked by the fact that tyre pressures increase as the temperature of the air inside them increases, lifting them above the pressures the system has "learned" as normal and exaggerating any disparity. I've seen it rise by as much as 0.4 bar. It may be possible to counter this by having the tyres filled with pure nitrogen rather than air (which is 80% nitrogen).
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