Tyre pressure monitor - showing low but pressures are the same both sides

[carolinewoodley]

HI Jeff,

Yes I'm getting a warning message (not a light) that does not go away. I didn't know about the MoT failure, I will tell them to sort it out before the car has its MoT. Yes it looks like it could be expensive, there was I hoping I'd have a cheap year with it not due for a service until next year! ;-(

They are also going to look at some white marks on one of the wheels anyway so at least that one will have to come off anyway.

Caroline

 

[Motorhead]

Caroline,

The fact that you're not getting the warning light would indicate that there isn't a problem with the TPMS, so you might get away with that on an MOT, although the recurring warning message is bound to be picked-up by Brooklands and possibly you could get away with an advisory. I presume that you've got the Porsche Extended Warranty, but unfortunately I doubt that will include TPMS battery replacement, although you might get lucky since I believe you only purchased the car last year and Brooklands could look favourably on rectifying your problem either FOC or at least for a reduced charge. It's certainly worth asking the question.

Just out of interest, do Brooklands have an in-house MOT test facility? Very few Dealerships do because they're very expensive to set-up and run and they can only charge a maximum of £54.85 to perform the test which, given that it ties-up a tech for about 45 minutes, means that it's a loss-leading operation with their eye-watering labour rates [up to £150/hour?]. My Cayman's MOT is due at the end of next month and I normally use Hatfield, who are about 40-miles away from me, to do the test as they have an in-house facility. I always wait for the test to be completed but in the current circumstances they want me to drop it off early morning to be be collected at an unspecified time up to 2-days later, so not very convenient. I think I'm going to find somewhere closer to home this time!

Jeff

 

[ralphmusic]

Jeff,

I use a local MOT place recommended by my Indy. I can see process start to finish and can talk about issues pre- test. Never going to use a Centre out—sourced tester again.

 

[Motorhead]

Ralph,

I know what you mean. A lot of people ask their PC to carry out an MOT not realising that they don't have an in-house facility and they just drive the car round the corner to "Harry's place" who gives them a discount and the Centre then charges the customer £54.85 for the process.

I've used a reliable family-run tyre, battery and MOT place in Bedford for many years for my other car, so it looks as though the Cayman will be heading off there this year too, although there are a couple of Indies in the vicinity I can contact for a recommendation. Thanks for the tip.

Jeff

 

[carolinewoodley]

OK so today I decided just to add a bit more air into the offending tyre and - hey presto! - the error message has disappeared [] HOWEVER - the absolute pressure now shows as 0.1 bar higher on that tyre than the other front one which doesn't have the error. Go figure!!

Anyway it means hopefully the error won't be there when the car goes in for its MoT, but if Brooklands can check the TPMS batteries on the extended warranty for free I will ask them to do so anyway.

The whole thing just mystifies me - my manual foot pump gauge was showing the tyre at 2.0 bar before I pumped it up a bit, whereas the TPMS showed it as 2.3, and as I've always assumed foot pump gauges are not that accurate I haven't really looked too closely at the figure before (as long as it looks about right that's where I've stopped pumping!) - but maybe that's more accurate and it actually WAS down a bit on that side?

I had assumed having the TPMS would make my life easier when it came to checking tyre pressures, but it seems it just makes it more complicated! [][]

 

[Brian_Innes]

Caroline,

I can understand your pain. The TPMS system is solely electronic based and relies on batteries and other electronic gismos to relay information to the driver.

I've always regarded TPMS as a guide only. I always take my tyre pressures with a hand held dial gauge using the old-fashioned tyre valve point as my reference. As Ralph will probably agree, taking tyre pressures at the valve is the preferred alternative to TPMS for some of us enthusiasts.

As for the MOT failure regulations if the TPMS fails, I must say I despair! I check my tyre pressures weekly with my pressure gauge. TPMS is only a warning system of an impending puncture as far as I am concerned. If my car failed the MOT due to a TPMS malfunction I would not be a happy chappie.

Brian

 

[carolinewoodley]

Hi Brian, I just checked online and it is an automatic fail if there is a "system malfunction" in the TPMS (https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/5-axles-wheels-tyres-and-suspension) - however it does say "You must only reject vehicles if it’s clear that the lamp indicates a system malfunction and not simply indicating that one or more of the tyre pressures is low" so it seems there is a get out if the tyre pressure is actually low (which seems more dangerous to me than having a malfunction where you can't rely on it - but hey whoever said Governments were logical?). Before last year it was considered a minor fail which is the same as an advisory in the old system (which I would agree with especially as I am not sure how reliable it is anyway).

Looking again the warning light *was* lit on the dash when the -0.1 bar message was on - sorry I had said the opposite earlier in this thread - but has gone away now it "thinks" the pressures are correct. So I would guess that would not have been an MoT failure as putting a bit of air in fixed the error and the light went away. However how would the MoT testers know this is the case and it wasn't actually saying the whole system had failed? Even the MoT guidance says different manufacturers' systems work in different ways so I guess that would mean they would have to know how each make's (and possibly model's) TPMS works?

I think I'm going to start doing the same as you Brian - to be honest, I've never been as diligent as you are for checking my tyre pressures for road driving (track days were a different matter, checked them on every session when I took the Caterham Seven on track) but if the TPMS error light is now potentially an MoT failure, and frankly I simply don't feel I can rely on it, at least I'd like to feel more confident that they are fine because I've checked them myself.

 

[Brian_Innes]

Caroline,

It's aways a worry when the TPM light comes on and there is no apparent reason for it doing so. The MOT failure regulation just makes it even more worrying and frustrating.

I recall I had a problem re-setting a TPM warning light when I swapped over the front wheels from side to side on my 718 CS. With the swapped wheels now rotating in the opposite direction, this caused the TPM to go into meltdown. My OPC gave me instructions to re-set the TPM system by selecting a different wheel size and driving for a few miles, then stopping, switching off the ignition, then re-setting the TPM with the correct size wheels and driving for a further 7 miles or so. This did the trick. My OPC also said that if this re-set procedure had failed, my TPM system would required a dealership service centre "hard re-set" with a lap top plugged-in.

What a bloody palaver caused by swapping the wheels I remember thinking at the time.

Perhaps you could also try the re-set remedy mentioned in a previous post. Sometimes these electronic systems get themselves into a knot.

Good to know you are also well versed in track day tyre pressure etiquette.

Brian

 

[ralphmusic]

..... My OPC also said that if this re-set procedure had failed, my TPM system would required a dealership service centre "hard re-set" with a lap top plugged-in...

Brian

Good job I’m getting PIWIS functionality....

 

[Motorhead]

Caroline, Brian,

Although generally I'm in favour of technology, sometimes it works against us, this being a prime example! Much depends upon the reliability of electronics, sensors, etc., and if [when?] things go wrong, chaos ensues, despite the general robustness of the systems. Personally I reckon that it was a mistake upgrading a TPMS warning from an MOT advisory to a fail - surely a physical measurement of the tyre pressures during the test would take very little time and confirm or otherwise the accuracy of the TPMS readings?

BMW were an early adopter of TPMS technology and I think warranty claims cost them a lot of money. It's a great technology when it works but I'm not convinced that its sophistication is entirely necessary for the majority of cars. The much simpler and more robust system on my old Mk5 Golf GTi uses data from the ABS wheel sensors to detect differences in wheel speed which occur when a tyre begins to deflate, giving a warning. A bit crude perhaps, but other than for very a rapid deflation as in a blow-out [for which TPMS wouldn't be any more useful] it's more than adequate.

Personally Caroline I wouldn't believe any foot-pump pressure gauge if my pump's gauge is anything to go by. Time to invest in a decent hand-held gauge I reckon.

Jeff

 

[carolinewoodley]

Personally I reckon that it was a mistake upgrading a TPMS warning from an MOT advisory to a fail - surely a physical measurement of the tyre pressures during the test would take very little time and confirm or otherwise the accuracy of the TPMS readings?

Yes agreed although the wording in the manual does seem to suggest that's what they *should* do if the light is on before failing a car (i.e. you should check it's not just because the tyre pressures ARE actually a bit low). I wonder how many MoT stations do though, especially if it is not a requirement of the standard MoT test? I would have thought with the pressures on getting an MoT done in a particular time frame most testers would only check whether the light was on, and unless they were familiar with that particular make and model of car and know that (as with the Cayman) the light shows up when it detects a slightly lower pressure, rather than *only* when the system itself malfunctions, I would take a fair guess that has led to a LOT of incorrectly failed MoTs - which of course go on the car's history.

Personally Caroline I wouldn't believe any foot-pump pressure gauge if my pump's gauge is anything to go by. Time to invest in a decent hand-held gauge I reckon.

LOL I have just bought a new one for this very reason, although I think you mentioned earlier on there is one in the Cayman anyway? But since I want to use it for my "daily driver" as well (which doesn't have TPMS at all) I thought I'd get a separate one.

 

[carolinewoodley]

Quick update on this, the car went for its MoT and passed no problem (the warning light had gone out anyway after I pumped the offending tyre up a bit), Brooklands reset the TPM and the tyre pressures are now showing OK and there is no error. So I am guessing it was just in need of a reset.

However I think in future I am going to trust the new mechanical gauge I bought rather than any sort of electronics! []

 

[Motorhead]

Pleased to hear that you’re all sorted Caroline. These electronic gizmos are great - when they’re working properly! - and it’s always handy if you can fall back on good old-fashioned methods. []

Jeff

 

[Spackers]

Just read this post for the first time. I had left my 991.2 in the garage for a few months because of a health problem. The Opc suggested pumping up the tyres above the normal level by 3psi and move occasionally. When I came to drive again I deflated to correct pressure using a good quality gauge. TPMS started by saying 3psi. keeps saying pressure is too high by 3. I suspect this system is not accurate. I’d rather rely on my gauge

 

[Motorhead]

Chris,

I think the best thing to do is perform a TPMS reset to see if that clears the problem. The system is pretty robust but as always with electronics, glitches can occur. It may be that when you’ve driven the car for a while the system will reset itself.

Jeff

 

[Spackers]

Thanks Jeff. Ill give it a try. Presume it’s the same as someone above mentioned which is to set tyres to different setting, restart engine then reset settings Back.

 

[Twinfan]

Yep, that's what I do but you don't need to start/re-start the engine. You can do it all with just the electrics on in one go.

 

[AndrewCS]

Agreed Jeff ... certainly has been for me, with various cars

Have thrice been saved from being stranded by immediate alarms / my monitoring. Really does pay to `read the manual up front`[]

I have a decent quality manual gauge and find that the Porsche and Ford systems relate extremely well and dare I say this, lead me to trust them [8D]

 

[Ray]

My vehicle is not fitted with pressure monitors. However, if it were, I would probably use the system as a guide and use my hand held pressure gauge to get an accurate reading.

If pressure monitors are fitted then I am sure people expect them to read correctly. What was the Porsche dealers response regarding the issue? There must be a tolerance of accuracy?

 

[JohnCRS]

When I did the reset on mine, it worked best if I set it for a different wheel configuration, drove it for 10 minutes and then switched back to the correct sizing. It seemed to make the system go through the full reset programme and resolved the issues.