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Discussion Starter #1
Or perhaps I should say, 'Tire Pressure Warning'. In the long learning curve of understanding the eccentricities of this otherwise excellent car, here's another.

I've never had a Tyre Pressure warning system, so was surprised when the light came on the first time. It was late at night and I stopped to check the tyres. None seemed flat, so I continued driving. The light went out before we got home.

When it came back a few days later, I checked all the tyres against the recommended PSI pressures: 35 front and 38 rear. Pretty much spot on but I adjusted until they were exact. Light still on.

After investigating the possibility of a light malfunction, I discovered the rather cumbersome instructions for a warning light 'reset'. A useful video on YouTube, and an even more useful set of instructions from a fellow PHEV driver on this forum. I tried it 20 times, each time requiring a short drive to lock in the reset. Nope, got rid of the light for a few seconds but it always came on again.

So, I took the car to a dealer today. It took them 5 minutes. The tyres were, they say, under-inflated. At least according to the readings to which the monitoring system was set. And guess what? This is different from the recommended tyre pressures in the handbook. They reset them to 38 PSI on all four tyres, and not what the handbook says.

Also, they told me that many pressure gauges, even the public ones in petrol stations, are often quite inaccurate. Their own are frequently calibrated by an external supplier to make sure they're spot on.

As I was using an old analogue pressure gauge / inflator, I stopped at Halfords on the way back and checked out what was currently available. The analogue model, there was only one, stated that it's accurate to within + or - 3 PSI. Together with the warning system looking for a level different from the one recommended in the handbook, it's surprising that this hadn't happened a lot earlier.

I now have a new digital gauge / inflator that claims accuracy to within + or - 1 PSI. Although the Mitsubishi dealer would probably cast doubt over that.

Life's an education. I hope this may save someone else the 20 plus attempts at fixing a problem that is really very easy to solve. But then that's what this excellent forum is for.
 

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.....As I was using an old analogue pressure gauge / inflator, I stopped at Halfords on the way back and checked out what was currently available. The analogue model, there was only one, stated that it's accurate to within + or - 3 PSI. Together with the warning system looking for a level different from the one recommended in the handbook, it's surprising that this hadn't happened a lot earlier.

I now have a new digital gauge / inflator that claims accuracy to within + or - 1 PSI. Although the Mitsubishi dealer would probably cast doubt over that.
The pencil type gauge, in which a volume of air displaces a cylinder, are actually far more repeatable for gauge pressure, and therefore more reliable of course, than electronic ones.

In a TPMS a silicon strain bridge detects an absolute pressure and a temperature gauge detects the local temperature. These are both transmitted to your car, and 'translated' into a gauge pressure. It is probably the changes in temperature rather than pressure that lead the TPMS to throw an error.

Also, as well you may have followed the book, but TPMS looks for differences in pressure. There is an assumption that you will have the front and back at the same pressure, and if they go out by more than 4psi then it'll flag an error. Obviously if you set them differentially to 3psi - as well you might because that's what the bl..dy manual says! - then you are going to risk an error at the slightest change in conditions.
 

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Discussion Starter #3
Thanks Donald. Intriguing information. I'm feeling ever so slightly smarter than I did when I got up this morning. By the time my lease runs out on this PHEV, I may actually understand it.
 

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Next time you're at your dealer I suggest you check with them exactly what they have set the tyre pressures at. Then without leaving, put your gauge on your tyres and see what the difference is. That way you get a free calibration of your equipment. In my experience the digital ones are quite accurate.
 

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I'm not very impressed by most of the integrated TPMS fitted to cars as original equipment. I like to know what the pressure in my tyres actually is. So on my last several cars I have fitted an external TPMS (Tyre Pal), that gives a proper pressure and temperature indication for each individual tyre and displays it on the dashboard. The indicator on the most recent version is solar powered so it needs no power connection and the sensor heads fit very neatly onto the rigid valve stems fitted to the Outlander.
It was interesting to note that initial inflation by the dealer showed 40 p.s.i. all round.
 

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Discussion Starter #7
Thanks Sagitar. 40 p.s.i. sounds like the dealer was crudely over-inflating to sustain the pressures over a longer period on the assumption that they'd all lose a little. Another confirmation that Mitsubishi dealers follow the way that the integrated TPMS works (assumes all 4 tyres have the same pressure) rather than what the manual advises (a difference of 3 p.s.i. between the back and the front). Perhaps one day they'll change the manual to catch up so drivers don't have to find this out by accident. Good tip about Tyre Pal. Thanks.
 

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I had a tyre pressure warning situation recently, nothing, but nothing would prevent it from recurring, but then I needed to have a tyre changed. Chap found that there was a fault on the TPMS on that tyre! He fitted a new one along with the tyre - hey presto, sorted!
 
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