Tyre pressure warning system.

[Nicksey]

I decided to do a quick pre winter check today. Tyre pressures are something I do about every 2 months regardless though. Normally they have been pretty good, only fluctuating by around a couple of pounds PSI.
However, knowing the weather was changing and the temp has changed markedly I knew this check was going to be an important one before a long trip on Friday. So, front tyres had dropped to 32 and 29! from the normal 35. That means a loss of 6 lb in the passenger front. At what point will the tyre deflation warning kick in?
On previous cars (Renaults) the system has let me know around the 4 lb loss mark. I checked the system, and all appears correct, the calibration is set and nothing looks untoward. The rear tyres had dropped to 30 from 33, which I think is ok for the weather changes. Surely there must be a limit before the system activates and lets you know?

[Kremmen]

The TPMS works on a check between all tyre rotation and if they have all lost the same pressure then no warnings are issued

I've noticed this for years on 3 Honda cars with TPMS

[Lord Voltermore]

Higher pressure means the tyres are slightly larger in circumference and do fewer revolutions per distance covered.   If all tyres drop equally  (or rise equally due to temperature) they will still be revolving at the same speed relative to each other.   The system cannot tell if the tyres are rotating (equally) faster because of pressure drop, or because you are driving that little bit  faster.   

The pressure drop overall is probably about normal if its been left a couple of months and the ambient temperature has dropped significantly.    But I am a bit surprised it didnt detect the difference of 29 and 32  on the front axle.  Did you check the 29 reading more than once?  Even with a reasonably decent pressure gauge I get the occasional rogue result.

Some may be concerned that the system doesnt detect  that all pressures  have dropped below what is recommended. . I am of the view that drivers should be checking their tyre condition and pressures regularly despite having  a TPMS.  Not  ignore them until a system tells them.   And the Honda system saves the problems and cost of  individual valve pressure sensors/transmitters  needing servicing, replacement etc. 

[embee]

One thing to check which is almost always overlooked is whether the valve core is actually tight.
I had a case of one tyre regularly losing a bit of pressure on a car, and embarrassingly didn't check the valve. Having taken the wheel off to check thoroughly for nails etc, I suddenly thought about the core and sure enough it was only just nipped up. A quick tighten with a valve core tool and problem solved.
Valve core tools are very cheap,  you don't need anything expensive for occasional private use.

[Nicksey]

I understand about all tyre pressures dropping simultaneously and equally, which given that all four corners are subject to the same weather and system changes...

However, one side front (passenger) had dropped 6lb and double what the other side had done. I am not concerned that there may have been a valve leak/puncture etc to cause this (there isn't and wasn't), the pressures were checked using the digital monitor at the pump AND with my hand held device too (both pre and post pump and both corresponded with each other.. I always check at home with the hand held device before visiting a pump), but why the TPMS didn't notice is concerning.

[Lord Voltermore]

The other three tyres all lost 3 PSI  - nice and consistent.   Not sure how you can say  the one that has lost 6psi over the same period  is not leaking .Either the valve  ,through the tyre rubber ,  tyre bead seal or a fault in  wheel itself.

As for the TPMS not detecting the pressure drop.  All the tyres have lost 3 psi due to natural permeation through the rubber over time  and the reduced ambient  temperature. Its the pressure of the other three tyres that sets the current  normal wheel rotation speed.   The 29psi tyre has only lost 3 psi more than the others  over the same period .Not  6 psi.   

I expect the tpms has a built in tolerance  to avoid too many false alarms.  . a discrepancy of 3 psi may be right on its limit of triggering the system .  As long as all 4 tyres  started off at  near enough the recommended   tyre pressures, a drop of just 3 psi on one tyre is not yet  significantly dangerous for braking or handling or harmful to the tyre. IMO

[ColinB]

Just a thought, but if the TPWS measures differences in rotational speeds, those differences will be greater at higher speeds. If you haven't driven at motorway speeds for a while, perhaps the differences haven't been great enough to trigger a warning. Most of the comments about false alarms seem to have happened at high speeds (which has also been my experience).

[Nicksey]

UPDATE:

Called into local dealer this morning, and found that the sensor was faulty. It should trigger the system if there is a significant difference in one corner over the other three.

Incidentally, there was no puncture, nail or leaking valve. The discrepancy I think was probably induced by my dealer, as it is not long ago that I had the second service (23k), and the tyres were checked during this time. I think they have failed to inflate correctly this particular wheel, thus causing the big difference.

New one ordered, to be replaced under warranty.

[guest13757]

The Honda Jazz Hybrids have a Deflation Warning System (DWS) as opposed to a Tyre Pressure Monitoring System (TPMS).  The difference is the former alerts to a deflation, whereas TPMS alerts to a change in actual tyre pressures.

DWS watches for deflation by monitoring each wheel and counting their rotations and constantly comparing the readings, and any change to the count i.e a deflating tyre, and it activates an alert.  It achieves this by using the ABS brake sensor, which is always counting rotations. 

A TPMS has a dedicated pressure sensor in each wheel/tyre assembly with a small battery and links to an alert system in the vehicle wirelessly.  It literally detects tyre pressure. 

I think the TPMS is the better system because it is actually measuring pressure in real time.  Whereas the DWS relies on deviations to wheel rotation counts with an algorithm to do the sums.  However I prefer the DWS because when the battery in the TPMS sensor goes dead it will be a visit to a tyre centre for a new one, and in addition when new tyres are needed you will be having a new sensors too – more cost.

I rotated my tyres front to back and sure enough the DWS alerted because the rotation counts were different from what it already knew, although all tyres were inflated to specification.  The system rightly recognised that the greater worn front tyres were now on the rear and the less worn rear tyres were now on the front.  So the system does work and it rightly recognised the previous counts were different.  Activating the recalibrate program and going for a drive reset the system and it was all good.

[Tombola]

I rotated my tyres front to back and sure enough the DWS alerted because the rotation counts were different from what it already knew, although all tyres were inflated to specification.  The system rightly recognised that the greater worn front tyres were now on the rear and the less worn rear tyres were now on the front.  So the system does work and it rightly recognised the previous counts were different.  Activating the recalibrate program and going for a drive reset the system and it was all good.

Sorry a bit off topic but as I understand it the tyres with the most tread are safer on the rear 

[guest10677]

Yes the 'Best' tyres should be on the back to mitigate overstear.

[guest13757]

My rationale for rotating tyres is to even out the wear to keep the tread depth on tyres uniform, which can help keep traction and handling consistent across all four tires over their life.

As for oversteer being mitigated by the best tyres on the rear, the opposite applies for worn tyres on the front and understeer then becoming a problem.  I am not sure which one I would prefer so I stick to the reasoning of keeping tyres uniformly worn with an occasional rotation.

In addition the Jazz Hybrid has an electronic stability system which will (within the laws of physics) mitigate over/understeer, and the more even the tread wear across all four tyres the better that system will function.