Yellow tyre pressure warning.

[Kremmen]

It certainly works.

I managed to get a screw in my rear nearside tyre and when the pressure had slowly dropped from 33 to 27 it got picked up.

[TnTkr]

All car's ECU are connected each other using a CAN-BUS network, so the ABS/ESP ECU (in our case the ECU performing the TPMS service) knows if the car is steering or if it's driving straight because the Electric Power Steering ECU shares the instant steer angle value to all other ECU such as ABS and NAVI. The system knows also HOW MUCH the car is steering and how much every wheel should rotate when you are curving, the front-external will be the fastest and the rear-internal the slowest, so the TPMS can detect a puncture also when the car drives on a long and slight curve.

I don't think it's that complicated i.e. so many values to take into consideration. I think the key filter to avoid unnecessary warnings is rather long time to calculate the average.

[jazzaro]

I don't think it's that complicated i.e. so many values to take into consideration. I think the key filter to avoid unnecessary warnings is rather long time to calculate the average.

TPMS system must consider these parameters, it must know if a wheel is running a little bit faster if it is losing pressure or if the car is on a curve like this: https://www.google.com/maps/@45.6937074,12.4971136,3a,75y,86.15h,81.74t/data=!3m6!1e1!3m4!1sQSovo6UJoFg8PcviVZB1zQ!2e0!7i16384!8i8192
The last puncture I had was discovered in less than 50mt.

[BeefOlives]

Would uneven tyre wear or an issue causing uneven brake wear set off the warning. I get the warning all the time on long journeys usually on the return trip and the first time the tyre pressure were off, but time after time the pressures have been fine. So now I just reset it and go.

Reason I ask it is after my mot today I've got one tyre front left at 3mm where the rest are 5-6mm and the right rear pad was completely worn affecting the disc. Also got slight binding on the front brakes. Wonder if any of that could be setting the thing off.

[Marco1979]

This can certainly trigger it!

It makes me think of someone who had an issue with his Civic Hybrid back in 2007. He could not activate cruise control and the engine would rev higher than normal. After months of search actions it finally turned out he replaced a front tire after a puncture and the difference in wear was so high the car’s onboard systems thought he was not driving straight ahead but in a constant corner…

Maybe your tires were changed in position in the past, one being more worn because of the sticky brakes, and that may set the alarm.

[Jocko]

I think a difference in tyre circumference due to one tyre being far more worn than the others can set it off.

[2robbie2]

My Toyota RAV4 has pressure sensing valves on all the wheels and still doesn’t tell me which one has dropped. To be honest, it doesn’t matter. It’s good practice to check them all anyway. Last time I had an alert, three tyres needed air. Back in 2003 I got a Renault Laguna top of the range and that could tell you which tyre was low. The graphic used to show the car with a wheel missing. It was very prone to false alarms and every time it showed us that graphic we’d all sing “Three wheels on my wagon”. I’m

I firmly agree - if the light comes on, it's good practice to just check them all at the same time - and not just the pressure - I find it's also a good opportunity to give the tyres a quick once over for any cracking or foreign objects - belt and braces and all that. 

[TnTkr]

I don't think it's that complicated i.e. so many values to take into consideration. I think the key filter to avoid unnecessary warnings is rather long time to calculate the average.

TPMS system must consider these parameters, it must know if a wheel is running a little bit faster if it is losing pressure or if the car is on a curve like this: https://www.google.com/maps/@45.6937074,12.4971136,3a,75y,86.15h,81.74t/data=!3m6!1e1!3m4!1sQSovo6UJoFg8PcviVZB1zQ!2e0!7i16384!8i8192
The last puncture I had was discovered in less than 50mt.

That is interesting. I wonder why it doesn't trigger the warning when front wheel is spinning due to slippery road. It can easily be more than 50 meters.

[Kremmen]

It probably needs more than a few seconds to make a decision ?

[jazzaro]

TPMS system must consider these parameters, it must know if a wheel is running a little bit faster if it is losing pressure or if the car is on a curve like this: https://www.google.com/maps/@45.6937074,12.4971136,3a,75y,86.15h,81.74t/data=!3m6!1e1!3m4!1sQSovo6UJoFg8PcviVZB1zQ!2e0!7i16384!8i8192
The last puncture I had was discovered in less than 50mt.

That is interesting. I wonder why it doesn't trigger the warning when front wheel is spinning due to slippery road. It can easily be more than 50 meters.

Because the way wheels slip is not the same: with a deflation, the wheel will have a slight difference and this difference will be constant or slightly increasing. During spinning, one or two wheels will have huge difference in rotation speed and this difference will vary very quickly. Rotating speed values are detected and calculated 25-30 times per second for each wheel (detection is very fast, hydraulic actuators are slower, now 10-15 times per sec),  the ECU can easily understand if there is spinning or deflation.
Consider that ABS ECU performs also the brake force  distribution between front and rear axle,  monitoring the rotating speed difference between front and rear while braking, so the detection is very precise. When ABS is working in a panic stop,  the ECU tries to keep the rotation speed at the 90% of the real speed if the tarmac is dry, 95-98% in wet road (in this conditions the grip is at maximum level) and the ECU understand if the road is wet or dry calculating how much time the wheel needs to re-gain its rotating speed after unlocking the brake caliper.
The  idea of ABS and hydraulic units were ready in the 80s, but ABS come only when industry could provide enough cheap, reliable and fast ecu (cpu, memories and ssr) to calculate the amount of data coming from all sensors.

[Lord Voltermore]

Having 3mm and 6mm tread on the same axle   is never a good idea.   It can cause uneven handling and uneven  braking performance. Even the same tread depth but different tyre brands/tread pattern is best avoided.       So  it may be  a good thing  if the tpms does activate. 

Easy for me to say, but if you need to replace a damaged tyre with a new one and the other tyre  is only 3 mm   its best to bite the bullet and replace both as a matching pair.  Most tyre experts recommend  replacing tyres at  3mm anyway, and even if you had hoped to continue  to  the 1.6mm legal minimum   3mm is already 78% worn. And many tyre suppliers give quite a good discount for 2 tyres compared to one. which can offset some of the loss.   
A difference may be ok  for a temporary spare, if you drive a bit more carefully. 

Michelin are the exception and imply their tyres are still adequate at 1.6mm.  But I doubt even they would recommend having different tread depths on the same axle.   

[Downsizer]

TPMS system must consider these parameters, it must know if a wheel is running a little bit faster if it is losing pressure or if the car is on a curve like this: https://www.google.com/maps/@45.6937074,12.4971136,3a,75y,86.15h,81.74t/data=!3m6!1e1!3m4!1sQSovo6UJoFg8PcviVZB1zQ!2e0!7i16384!8i8192
The last puncture I had was discovered in less than 50mt.

My back of envelope arithmetic suggests that driving a complete circle, regardless of the diameter, would result in the outer wheel travelling roughly 8m further than the inner wheel.  The same difference would result from travelling only about 350m with one tyre deflated to the extent of a 3cm reduction in diameter.  I think a much longer distance (or a flatter tyre) is needed to trigger the warning.

[John Ratsey]

It probably needs more than a few seconds to make a decision ?

Yes, there's a time / distance delay to avoid false alarms due to wheelspin or bends. I recall someone here (or maybe in the HR-V forum) reporting that they had to replace a tyre because the missus didn't notice it was flat before driving off and had driven ?100? metres before the TPMS issued an alert.