Tyre Pressure warnings....danger of crying wolf too often

[peteo48]

That's my thinking John. As you check the tyres there is, inevitably, a small loss of pressure and you may also put a pound or two in to bring them up to the specified level.

I'm certainly going to run with this method for a bit. If it keeps coming on, I think there must be something wrong with it and, at that stage, I'll take it in.

[ColinB]

It should not be necessary to keep re-calibrating, nor to put up with repeated false alarms. Personally, I would get the dealer to check it under warranty, that should bowl out whether there is a system fault.

Assuming the dealer reports no fault, then there must be something causing the system to detect differing rotational speeds, which it interprets as different tyre pressures. Some random ideas:

1. There are a couple of queries on Honest John that seem relevant:
https://www.honestjohn.co.uk/askhj/answer/59369/tyre-deflation-warning-system-malfunction
https://www.honestjohn.co.uk/askhj/answer/69714/honda-jazz-tyre-deflation-system---is-there-a-problem-
In both cases the suggestion is that there might be a slight unevenness between tyre pressures so that one of them triggers the alarm when it gets hot at speed. He seems confident that trial-and-error adjustment of pressures ought to fix it (which introduces the interesting question of how accurate is the pressure gauge you're using ?).
2. Could there be something about one wheel that causes it to heat up (or cool down) at speed more than the others ? Would a brake pad that doesn't quite lift clear of the disc do that ?
3. Would a slight wheel imbalance affect the rotational speed so as to trigger the alarm ?

I have no reason to think that any of these is the likely cause, just suggesting that if the system is working correctly then it is probably genuinely detecting some lack of symmetry between the wheels, your problem is finding it.

[culzean]

I have never had 'false alarms' on either Jazz or Civic - if there has been an alarm it has been for a reason, new tyres fitted or changing from summer to winter tyres and back (even then not on the Jazz, only the Civic).  I have had proper alarms when pressure has dropped 5psi with slow puncture so that is quite sensitive.   If system is not happy with ABS pulses it is receiving the TPMS icon is supposed to flash.

Accuracy of pressure gauge should not really matter to TPMS if you are using the same one for all four wheels (although it does matter to your tyres).  Some of the newer models of ABS based TPMS (iTPMS = intelligent TPMS) may have ''spectrum analysis' software which can apparently pick up irregularities in the ABS signals caused by all tyres being under-inflated (like when you just ran over a police stinger LOL).  If you have iTPMS (don't know if MK3 Jazz has it)  it may be that the software is not behaving correctly.

[ColinB]

Accuracy of pressure gauge should not really matter to TPMS if you are using the same one for all four wheels (although it does matter to your tyres).

What I was trying to get at (poorly) is this: let's say your pressure gauge is accurate to +/-2psi (which is probably significantly better than the average garage airline). If you use it to check and reset all your tyres to the same nominal value, it is conceivable that one tyre may actually be 2 psi below that value, another may be set 2 psi above despite the gauge reading the same in both cases. As the tyre heats up at speed, that pressure difference will increase and might be enough to trigger the TPMS. If the TPMS is "intelligent" such that it also monitors absolute pressure as well as (or instead of) relative pressure, then a tyre that's been accidentally over-inflated due to gauge inaccuracy would obviously breach any upper limit as it heats up before any tyres that have been under-inflated ... which ought to trigger the alarm.

That's all complete speculation and may be utter rubbish, but it seems plausible to me, it fits with Honest John's theory, and might help explain why some people are seeing this but not others.

[guest4871]

I think that it is the gauge that is +/- of  a standard.

If you use the same gauge on all the tyres they will all be the same +/- of the standard because the gauge will have a constant error to the standard.

Therefore all the tyres will be the same pressure at the same reading on the gauge.

[Jocko]

I think that it is the gauge that is +/- of  a standard.

If you use the same gauge on all the tyres they will all be the same +/- of the standard because the gauge will have a constant error to the standard.

Therefore all the tyres will be the same pressure at the same reading on the gauge.

Correct.

[peteo48]

I think that it is the gauge that is +/- of  a standard.

If you use the same gauge on all the tyres they will all be the same +/- of the standard because the gauge will have a constant error to the standard.

Therefore all the tyres will be the same pressure at the same reading on the gauge.

Indeed. And that was my thinking behind going round the whole car and setting them at the recommended pressures. Each tyre, on each axle as it were, is inflated to the same level. I had already checked wear and it's pretty uniform (the car has only done 7500 miles).

So, if it goes off again, and the tyre pressures are all the same and no punctures, the system is definitely giving out false alarms.

Clearly it's a problem with this particular system but what I haven't yet been able to find is an example of somebody who has had this issue solved and how it was solved.

I'm hoping my issue will "go away" as it has with others.

[Downsizer]

Accuracy of pressure gauge should not really matter to TPMS if you are using the same one for all four wheels (although it does matter to your tyres).

What I was trying to get at (poorly) is this: let's say your pressure gauge is accurate to +/-2psi (which is probably significantly better than the average garage airline). If you use it to check and reset all your tyres to the same nominal value, it is conceivable that one tyre may actually be 2 psi below that value, another may be set 2 psi above despite the gauge reading the same in both cases. As the tyre heats up at speed, that pressure difference will increase and might be enough to trigger the TPMS. If the TPMS is "intelligent" such that it also monitors absolute pressure as well as (or instead of) relative pressure, then a tyre that's been accidentally over-inflated due to gauge inaccuracy would obviously breach any upper limit as it heats up before any tyres that have been under-inflated ... which ought to trigger the alarm.

I'm not certain that an overinflated tyre heats up more than an under inflated one.  It might be the other way round; I've forgotten the relevant physics!  The lower pressure one will certainly flex more.  Either way, it doesn't alter your speculative argument.

[sparky Paul]

I'm not certain that an overinflated tyre heats up more than an under inflated one.  It might be the other way round; I've forgotten the relevant physics!

You are quite right, the flexing of the tyre walls makes the under inflated tyre heat up.

[ColinB]

I think that it is the gauge that is +/- of  a standard.

If you use the same gauge on all the tyres they will all be the same +/- of the standard because the gauge will have a constant error to the standard.

Therefore all the tyres will be the same pressure at the same reading on the gauge.

Nope. If a gauge has a tolerance of plus or minus a few psi, it can read anywhere within that range. There is absolutely no reason why it will always read high or low so you cannot assume that all tyres are at the same pressure.

However it’s clearly not worth labouring the point further, it was simply a thought about what might be contributing to the issue reported.

[ColinB]

I'm not certain that an overinflated tyre heats up more than an under inflated one.  It might be the other way round; I've forgotten the relevant physics!

You are quite right, the flexing of the tyre walls makes the under inflated tyre heat up.

Basic physics. Recommend revising Gay-Lussac’s law. Pressure is proportional to temperature. So if you have two tyres, one over-inflated and one under-inflated, and subject them both to the same temperature rise, the pressure differential will be proportionately greater after the temperature rise which may be enough to trigger the TPMS.

Whether that would be cancelled out or reversed by any tyre flexing is an interesting point. If that effect is significant, it might work against the TPMS because a reduced pressure would - via sidewall flexing - raise the temperature in the tyre which would tend to increase the pressure and inhibit the TPMS. I suspect there’s a PhD thesis in there somewhere to work out exactly what might be going on.

[culzean]

I think that it is the gauge that is +/- of  a standard.

If you use the same gauge on all the tyres they will all be the same +/- of the standard because the gauge will have a constant error to the standard.

Therefore all the tyres will be the same pressure at the same reading on the gauge.

Nope. If a gauge has a tolerance of plus or minus a few psi, it can read anywhere within that range. There is absolutely no reason why it will always read high or low so you cannot assume that all tyres are at the same pressure.

I tend to agree with zzaj on the + or - error tending to be in the same direction (like the error on a speedo), especially on a mechanical type gauge (stick or dial type), what can make a difference is hysteresis (where depending whether the pressure is rising or falling the device will measure a different value,  but the pressure is rising and then constant when you measure a tyre pressure). Hysteresis would only make a difference if you left the gauge connected and then raised or lowered the pressure in the tyre by another means ( ),  and depending if you raised or lowered the pressure the gauge would take up a different reading.   I think sometimes as well the reading of a digital gauge can be affected by the condition of the battery, and in cheaper gauges the resolution of the analogue to digital converter may be dependent on the price you paid.

[Jocko]

At one stage of my career, testing and calibrating measuring equipment was part of our remit. What we found was, though a piece of equipment would be within its +- 2% limit (for example), repeatability would be within about a tenth of that. So once you knew how far out a piece of kit was, you could make an allowance and get a fairly reliable reading.

[Skyrider]

My guess is that it is a calibration error rather then a tyre pressure problem. Are the alarms regularly 30 minutes driving time from a calibration? Are you getting a " Calibration complete" message in the multi function display after a calibration?

[peteo48]

I am getting the "Calibration Complete" message after a calibration. The only pattern to the false alarms I've had so far is that they have occurred after a shortish spell of motorway driving.

I've only had 2 false alarms so possibly not enough for a reliable pattern to emerge. After this last one, I have very carefully checked the tyre pressures and equalised them where necessary. Done a recalibration after that so I'll see what happens now. I gather the recalibration is not actually complete until you've covered a certain distance after setting it.