Tyre pressure warning...

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BarryWhitt

Member
Joined
Feb 28, 2017
Messages
43
Location
North Cambridgeshire
Car
C-Class 200 Sport Premium
In my face on the speedo that I must check my tyre pressures. 228 kPa front and rear nearside and 235kPa front and rear offside.

That's in real terms 1.0153 Psi difference!

Seems OTT to me....your views please.
 
I agree.

First time I saw it I thought I must have a puncture as the difference in pressure looks significant until you work it out in PSI.
 
Is it the pressure difference or is it that the pressures have dropped below the set limit, due to the colder weather?
 
Inside fuel flap its say 250kPs/36psi all round for 2-3 people in car, then up to 5 with luggage 270/39 front 310/45 rear.

I've just done 250/36 all round and warning light has gone out. :)

But the pressure went up after doing a couple of miles, which is normal.

Thanks.
 
That's good. The system has done it's job as your tyres were under inflated and it's told you about it. In case you were wondering how it works, the valve has a sensor on the end inside the tyre. You may have noticed the valves were metal rather than rubber. Take care with them as they are £45 each! Inside the sensor is a small battery which activates once the wheels start rotating to power the singal. This battery lasts around five years until it conks out. At that point you have to replace the valve unfortunately.

This is what they look like. Ignore the part number.

HTB1P2yANpXXXXbuXXXXq6xXFXXXB.jpg
 
A couple of years ago I had a very slow leak in the rear offside tyre. So little it would only lose a couple of psi in a month. Due to the fact it doesn’t get used from one week to the next every time I did go out in it the warning would come up on dash, I’d stop in garage, top it up and it’d be fine for another few weeks. Problem was it was kind of crying wolf because I was on my way to msl Birmingham one day with a friend and up came the warning while doing 70 on the m1. I turned round to him and said it’s ok it always does that. Pulled in garage a couple of miles ahead and tyre was flat and smoking. Didn’t even feel it.
 
Sorry. Double posted for some reason.
 
That's good. The system has done it's job as your tyres were under inflated and it's told you about it. In case you were wondering how it works, the valve has a sensor on the end inside the tyre. You may have noticed the valves were metal rather than rubber. Take care with them as they are £45 each! Inside the sensor is a small battery which activates once the wheels start rotating to power the singal. This battery lasts around five years until it conks out. At that point you have to replace the valve unfortunately.

This is what they look like. Ignore the part number.

HTB1P2yANpXXXXbuXXXXq6xXFXXXB.jpg

These sensors can have their battery replaced, if you're handy with a scalpel and sealant. I beleive they take a tagged CR2450 button battery.
 
This battery lasts around five years until it conks out. At that point you have to replace the valve unfortunately.
You're having a bl**dy laugh aren't you.

Didn't realise the TPM was that sensitive,I can get the reading up quite a bit on one side by bombing round a few left handers. :D
 
As long as the cold pressures are correct the in use pressures will always be within design limits
 
These sensors can have their battery replaced, if you're handy with a scalpel and sealant. I beleive they take a tagged CR2450 button battery.

Thanks. Didn't realise that. Still a ballache isn't it?
If they made the battery easy to get to, you could just pop a new one in at each tyre change.
 
These sensors can have their battery replaced, if you're handy with a scalpel and sealant. I beleive they take a tagged CR2450 button battery.

I was wondering about this, mine are seven years old now and still working fine, perhaps they’ll need replacing soon...
 
Seems OTT to me....your views please.
The pressure difference that's triggering the warning is not that between the individual tyres, but instead from the reference value that was set when the Tyre Pressure Monitor was last restarted.

When you adjust/set your tyre pressures you should always restart the Tyre Pressure Monitor so that it has a baseline set of pressures to work from.
 

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