TPMS Sensor issue !

[Watch-Collector]

I am not getting any pressure readings for any tyres on the dash and the TP warning light is on . On a Snap on diagnostic device it picks up pressures for all 4 tyres .I have tried to reset the system but to no avail . Could it be a low battery on one of the sensors which is throwing out the whole system . Porsche say they can diagnose the battery life on the TPMS sensors but I dont want to go that route if its an easy fix !
If anyone has had the same issue and would be kind enough to advise it would be much appreciated :-)
Thanks

Edited by Watch-Collector on Friday 12th May 14:21