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Technical Tyre Pressure Monitoring System

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Technical Tyre Pressure Monitoring System

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James The Butler

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The TPMS light came on a few miles from home today; a quick visual check showed nothing to give immediate alarm. On arrival home, I left things for an hour and then checked all the tyre pressures, they are spot on (I have contributed to a past debate about what the TP's should be) so I simply reset the system on the menu. I turned on the ignition and the warning light and buzzer came on again, I then started the car thinking this might clear it, but no. I then put '12 foot pump strokes of air into each tyre to see if that subtle change would assist. No, the warning buzzer and light are still coming on. Your thoughts appreciated please. Happy New Year to all members.
 
The system doesn't actually measure (or know) the pressures, so adding air will not affect it. What it senses is one wheel rotating at a different speed to the others (by, as already answered, using the ABS sensors to measure wheel speed). If one tyre is markedly soft, that wheel will have a different rolling speed to the others.

Starting the engine wont change anything either. But if you have reset it, the warning should go out. You need to be moving for it to sense a soft tyre, so if it didn't cancel, either you didn't complete the reset, or something else is amiss.
 
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Herts Hillhopper said:
The system doesn't actually measure (or know) the pressures, so adding air will not affect it. What it senses is one wheel rotating at a different speed to the others (by, as already answered, using the ABS sensors to measure wheel speed). If one tyre is markedly soft, that wheel will have a different rolling speed to the others.

Starting the engine wont change anything either. But if you have reset it, the warning should go out. You need to be moving for it to sense a soft tyre, so if it didn't cancel, either you didn't complete the reset, or something else is amiss.
Click to expand...
Oh, wow. I totally thought the tom knew when a tyre pressure dropped, thanks for explaining it doesn't !
Guess you still need to check tyre pressures regularly then?
Thanks
 
Herts Hillhopper said:
Read the handbook- page 66 in my edition - which specifically tells you that it cannot take the place of the owner checking the pressures regularly. It also explains, very badly, how to reset it.
Click to expand...

I agree you MUST check your tyres. The TPMS only activates when the pressure has dropped VERY low. Trial and error suggests down as low as 5PSI. Although the tyre will look like there is air in it - but soft - the car would be dangerous at this level. It hopefully will stop you driving off from rest if a tyre has deflated totally and prevent you needing a new tyre instead of a repair.

For good steering and braking tyres need to be correctly inflated and checked as you say.

Space savers need more pressure and are lethal if not correctly inflated.
 
First, many thanks all for your contributions. I should have said that, being old school, I do check the tyre pressures/fluids weekly. Yesterday I double checked the TP's at lunchtime (tyres stone cold) they were OK, reset the system and drove home - about a 20 minute drive. The warning light stayed on. My excellent local garage have the car today and have just called me to say that there is no problems either with the condition of the tyres or the pressure settings. They said that I'm the fourth car this week to come in with a TPMS system light showing and speculated about change in road surface temps being the cause. I'm now wondering if there is a fault with the sensor, but I don't want to be driving around under a 'false flag' of the warning light still showing.
 
The ‘sensor’(s) are the ABS brake system sensors. If a problem with them, various other warning lights (inc the red ‘brake’ warning light) should come on too. Do you see the ‘confirmed’ message when resetting the TPMS warning?
Apparently the system can be fooled by a harsh bump in a pothole, where the speed of one wheel momentarily alters compared to the others.
 
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The Panda Nut said:
I agree you MUST check your tyres. The TPMS only activates when the pressure has dropped VERY low. Trial and error suggests down as low as 5PSI. Although the tyre will look like there is air in it - but soft - the car would be dangerous at this level. It hopefully will stop you driving off from rest if a tyre has deflated totally and prevent you needing a new tyre instead of a repair.

For good steering and braking tyres need to be correctly inflated and checked as you say.

Space savers need more pressure and are lethal if not correctly inflated.
Click to expand...

Depends on the car but mine come on at around 5-6psi difference
 
Thanks again; my local garage (a good 'un) found no fault. When I picked up the car tonight the warning light was not on - they had reset the TPMS - and I went out for a 20 minute drive. Problem gone away but that's interesting to hear about the bad road bump scenario. There we no other warning lights shown throughout. To all many thanks for your help.
 
James The Butler said:
First, many thanks all for your contributions. I should have said that, being old school, I do check the tyre pressures/fluids weekly. Yesterday I double checked the TP's at lunchtime (tyres stone cold) they were OK, reset the system and drove home - about a 20 minute drive. The warning light stayed on. My excellent local garage have the car today and have just called me to say that there is no problems either with the condition of the tyres or the pressure settings. They said that I'm the fourth car this week to come in with a TPMS system light showing and speculated about change in road surface temps being the cause. I'm now wondering if there is a fault with the sensor, but I don't want to be driving around under a 'false flag' of the warning light still showing.
Click to expand...

The Only time I have ever had a light in miles and cars was after a garage broke a sensor at service. They reset the system and sent the car out.... 10 miles later on the light came on. Anyway a new sensor was fitted and the problem went away. I suspect a faulty sensor is possible. In my case the valve cap corroded and when turned very hard to get it off it damaged the sensor.
 
The Panda Nut said:
The Only time I have ever had a light in miles and cars was after a garage broke a sensor at service. They reset the system and sent the car out.... 10 miles later on the light came on. Anyway a new sensor was fitted and the problem went away. I suspect a faulty sensor is possible. In my case the valve cap corroded and when turned very hard to get it off it damaged the sensor.
Click to expand...
That would be on a car with individual sensors in the tyre valve. The Panda doesn’t have these
 
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