Hi,  When I first got my 64 plate Focus Titanium X the tyre pressure monitoring system alerted me when one of my tyres was under inflated.   I don't get an alert anymore even when one of the tyres is 5/6 psi under inflated.  I always pump the tyres up to 31 psi and reset the TPM system which is stored.  Ive not had any tyre changes so I know it isn't to do with that.  Anyone else experienced this problem and if so , how did you fix it.   Thanks.

Try letting 1 of the tyres down to say 15psi and start engine and see if it alerts you, could be that 5 or 6 psi is not enough to throw a discrepancy for the monitor to alert you. 

Is it TPMS or DDS? They're not the same.  DDS seems a lot less sensitive and I believe uses the ABS system to calculate problems.  It definitely does need resetting each time and as above, try letting 1 tyre go right down.

It used to let me know when a tyre deflated to 27.5 psi.     And yes, as far as I know it is TPMS

if it is tpms( you can tell by looking or feeling for a ridge around the rubber valve ) then the trigger point is at least 20% of the warm tyre learnt value. so at 31psi triggering should occour approx at 24psi or so. thats assuming your tyre gauge is reading correctly thoughout its range. alot of guages dont. 

Okay, thanks for that info Iantt.  Sorry for delay in replying - been away.