BMW 330i Tyre Pressure Monitor

[TheBinarySheep]

I have a 2019 330i on 19 inch wheels. Tyres are Pirelli P Zero Run Flats.

A couple of days ago the car flagged up that the drivers side front tyre pressure was low. I checked, and it was 2.1bar vs 2.3bar of the one on the passenger side. I put some air in so both front tyres were the same pressure, and I reset the TPM.

I've driven the car this morning, whilst also keeping an eye on the tyre pressures, and they were all showing green @10c. Fronts were both 2.2bar and rear were 2.0bar.

After a while, the car has flagged up that the rear passenger side tyre is low on pressure now.

Can anyone confirm how this system works? I always thought that it notified you when there was a significant drop in tyre pressure, but that can't be the case if pressures didn't drop after I'd reset it, and even so, surely the system takes into account temperate drops?

The car itself is recommending that tyre pressures be 2.7bar, but it doesn't say at what temperature.

[ScoobyChris]

My experience of the system is it flags up low when there is a greater than 0.2 bar drop in tyre pressure from the pressure the TPMS is set to and it doesn't appear to account for temperature changes in that. The recommended inflation pressure is when the tyre is "cold" but reading around there seem to be lots of schools of thought on what cold actually means - in practice I do it first thing in the morning.

Chris

[TheBinarySheep]

ScoobyChris said:

My experience of the system is it flags up low when there is a greater than 0.2 bar drop in tyre pressure from the pressure the TPMS is set to and it doesn't appear to account for temperature changes in that. The recommended inflation pressure is when the tyre is "cold" but reading around there seem to be lots of schools of thought on what cold actually means - in practice I do it first thing in the morning.

Chris

That's the thing, I reset it when I got in the car this morning when the tyre temps were only 8c. I'd driven a couple of mile, temps had risen to 10c and then it flagged up one of the tyres was low, but it's a different tyre to what it was flagging up the other day.

[E-bmw]

TheBinarySheep said:

That's the thing, I reset it when I got in the car this morning when the tyre temps were only 8c. I'd driven a couple of mile, temps had risen to 10c and then it flagged up one of the tyres was low, but it's a different tyre to what it was flagging up the other day.

Just because it is a different tyre doesn't mean there is something wrong.

Best advice:

Set ALL pressures exactly correct when cold together at the same time.

Use the pressures in the manual/drivers door pillar, reset the system & then see what it says, if it flags up a tyre recheck it to see if there is a genuine reason for it.