Random TPMS Errors?

Technical Forum for the Porsche Macan
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nsm3
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Post by nsm3 »

Had a front, offside tyre warning the other day, down -0.4 bar. Pulled up, checked tyres and all seemed well. Switched on/off but warning still there. Loss dropped to -0.3 bar and after 2 miles it cleared. Happened again later in the day. Checked all the pressures the day after and all were equal across the axles and only a couple of PSI down on set point, certainly not 1/2 bar adrift? Hasn't re-occurred yet, but after driving for 42 years without a TPMS system (even managed a 70mph blow out on the M6 in an Austin Ambassador once!), I can't say that I have a lot of confidence in the system?

Is this another 'they all do that Sir' thing, or has anyone experienced this as something that needs attention/repair?
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GMAN75
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Post by GMAN75 »

Tyre pressure isn't a constant thing. For one thing, it changes with temperature. Given the country, and its roads, have gone through extremes recently, I don't think such a small change is out of the norm.
johnd
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Post by johnd »

I think what happens is that over time the tyres do very slowly leak air and lose pressure. It may be only eg 0.1 bar every 2-3 months but it does seem to happen on at least some tyres or valves.

If you then couple that with the fact that the mornings will be starting to get cooler in the coming weeks and hence tyre pressures dropping and one day you'll get to the point where the deviation from the preset value in the TPMS changes from -0.2 to -0.3 (or is it -0.3 to -0.4?) and hence from being oblivious (probably) to the TPMS readings you suddenly notice a warning. It feels like there's a puncture or something but in reality all that's happened is that the combination of very slight pressure loss and lower temperatures has just crossed the threshold where the alarm is triggered (although if you had been religiously monitor the pressures every day, you might have noticed that you were getting close to the warning).

Probably within 5-10 minutes of driving, the tyres will have warmed up enough to switch the alarm off again.

Of course, none of this means that one day you might not really have a puncture.
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Col Lamb
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Post by Col Lamb »

What I have done for quite a few years if I have had a persistant fault is to get the tyres warm, then reduce pressure by about 10 psi, tighten up slightly the valves and then refilled to about 2 psi above normal.

Put the car or bike away, then next day on cold tyres, adjust tyre pressures.

This has cleared the fault on a few cars and bikes when it has happened and simply resetting has not worked.
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davewf
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Post by davewf »

Had same issue exactly but that was on a very hot day, settled down on its own and not occurred since. I did check pressures manually and made sure they were all correct,
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nsm3
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Post by nsm3 »

Cheers all, guess I need to be a bit more vigilant on monitoring my tyre pressures and not just rely on the warning system?
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Paul
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Post by Paul »

I tend to check mine “ properly” with a guage once a month (ish😊) but I do find the TPM very accurate. 2.3 / 2.5 tends to creep up to 2.5 / 2.7 in use (as I would expect) - a bit higher recently in our exceptionally hot weather, but I’m now anticipating putting in a few 1/10 of a bar as the weather cools and the tyres have certainly “ lost” a few through normal usage.
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Nuclear Nick
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Post by Nuclear Nick »

Oxygen permeates the rubber so pressure will drop over time even if there is no puncture or rim/valve seal issue. It's one of the reasons pure nitrogen is used by some.
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