Living in rural Scotland, I put winter tyres on my Fiesta around this time of year and to make this simpler, I have two sets of alloys, one with each set of tyres. I've had the car for a few years and previously, I have had new TPMS sensors installed when I bought new tyres as they were probably the factory fitted ones and quite old (it's a 16 plate) - two sets since I bought the car and I've had to program the sensors after installation.

Yesterday, I put the winter wheels on and afterwards, fired the car up expecting to hear the TPMS warning and then going through the reprogramming process but there was no warning. I thought that maybe I had to trigger them by driving but still no warning. It just crossed my mind that maybe the sensors in the wheels I took off were detected as they were stacked just a few feet away but that would not explain why they were detected when I took a drive. Up until now, the car's system has been pretty aggressive (and annoying) with its warnings.

So, I'm wondering if previously installed sensors are 'remembered'. It's the only explanation that I can think of for the warnings not going off.

The car already knows the wheels / sensors (your winter wheels) from the last time you had them fitted.

If it was not detecting the TPMS sensors in the wheels that are now fitted then the tyre pressures would show "--"

You can check the TPMS using FORScan.

Okay, that's what I thought.

However, on my Fiesta, the tyre pressure is not shown and although each sensor is paired with a wheel position, when the system tells you to check the tyre pressure, it does not tell you which tyre so you have to check them all.

Just out of curiosity, how many sensors can it theoretically 'remember'?

I haven't used FORScan for a while because there were problems with renewing licensing and it's so long that I don't think I have a computer with Windows installed anymore to run it.

Okay, that's what I thought.

However, on my Fiesta, the tyre pressure is not shown and although each sensor is paired with a wheel position, when the system tells you to check the tyre pressure, it does not tell you which tyre so you have to check them all.

Just out of curiosity, how many sensors can it theoretically 'remember'?

I haven't used FORScan for a while because there were problems with renewing licensing and it's so long that I don't think I have a computer with Windows installed anymore to run it.

Unfortunately, I was out in the car today and got a 'Tyre Monitor System Malfunction - Service Required' warning.

As soon as I got home, I got my programming tool out and went through the usual procedure and all the tyre sensors were recognised so I suspect that they had not been remembered after all.