TPMS sensor missing? No Alert.
 

I'm getting new tires put on my 2010 Cooper S hardtop and the shop that's installing the tires just called to tell me that one of the tires was missing a sensor.

I've had no alert in the dash telling me about a missing sensor (MINI dealer assured me that an alert would go off if I were missing a sensor), and the tire guy said maybe it was bypassed because a screw/bolt was installed right into the end of the valve stem.

Thoughts?

I don't know if this is a rear or front tire.

Do all four tires tell air pressure the same way or do the back tires work on speed and/or pressure?

Do I need a new sensor there?

A great tire deal has just jumped up by $100 in price.

Help.

Thanks!