TPMS Fault

[Mario]

Hi all, got a front blowout today and initially the car just called out that tyre as being flat.

Then managed to fit a space saver to the rear and moved the rear wheel to the front.

Drove the car back a few miles and got the error ‘TPMS Tyre pressure: fault. See owner's manual’

Is this just because of the space saver? The car has standard rubber tyre valves (not metal TPMS ones) and the only option in the MMI is to store tyre pressures, not view any temps or pressures.

So I am assuming this is an ‘indirect’ (wheel speed) system.

Anyone know if the fault will clear when I get a new tyre?

The space saver is 120/70/R19 (658mm diameter) and the normal tyres are 245/40/R19 (678mm diameter)

Would this 20mm smaller diameter cause this fault?

Also I have a full spare set of wheels from an older Audi B8…if I fit them temporarily will the fault clear??

They are 235/45/R19 (693mm diameter)…will I need to fit all 4 or would just 1 work?

Main query is…should I be concerned at all over this issue? No other faults, just this TPMS one that will not clear even if I set pressures and store them via the MMI.

Not sure if it needs to ‘see’ good wheel speeds before self clearing and an MMI pressure storage is insufficient??

 

[Mario]

Guess I can answer my own question here incase someone else wants to know.

I changed both rear wheels with my spare set from an A4 B8 (255/35/R19 = 660mm diameter)

Stored the pressures and drove the car. After 2-3 miles the TPMS fault cleared! So the car was understandably unhappy with the rear left and right wheels being different diameters / circumference.

I have now noticed if I accelerate harder than normal the traction control is kicking in but that is 99% because the car is seeing the rear rotating faster than the front (660mm rear diameter vs 678mm front diameter) and thinks the rear wheels are losing traction when they are not (car is a Quattro variant).

I assume that traction control intervention will stop once all 4 wheels are the same size.