How do the tire air valves affect the inflation pressure alarm?

Are they green caps, from Costco?

My rule #1 when going in there: take the valve caps off beforehand.

But anyway, any half-decent cap will be effective. They're mainly to keep the valve clean. And provide a slight second-line-of-defence against air leakage, I suppose.

 

The valve caps have nothing to do with the TPMS warning system. If your original caps were metal and now they are plastic, that's a downgrade. But plastic for plastic, probably not worth worrying about.

 

OEM are very flat-topped, metallic looking, but actually plastic. I read somewhere metal caps are bad for something, causing valve stems to rust, or?

 

The metal ones I've had were aluminum, so no worries about rust.

 

Not really up on it, but reading a bit, see some talk about dissimilar metals. If you frequently take them off to check pressures (always a good idea) then not time for anything to seize I guess. But hey, think I'll stick with plastic.