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Noise from rear axle

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Old Jul 6th, 2019, 06:48   #21
id5
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The technicians currently reckon that the reason the TPM does not work is due to a dirty ABS sensor. It begs the question of why the little goblin in the engine bay sees that the car is moving forward but does not notice that the ABS doesn't see the wheels turning. If it did then it could tell someone that one of the safety systems, the ABS, is not working correctly.

The ABS sensor has been cleaned and I have been asked to see if the fault occurs again. If it does then the next step is apparently to replace the drive shafts.
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Old Jul 8th, 2019, 19:12   #22
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Quote:
Originally Posted by id5 View Post
The technicians currently reckon that the reason the TPM does not work is due to a dirty ABS sensor. It begs the question of why the little goblin in the engine bay sees that the car is moving forward but does not notice that the ABS doesn't see the wheels turning. If it did then it could tell someone that one of the safety systems, the ABS, is not working correctly.

The ABS sensor has been cleaned and I have been asked to see if the fault occurs again. If it does then the next step is apparently to replace the drive shafts.
I'M with you on this....I can't see ANY way in which the ABS sensor can assist the car in knowing what the tyre pressure is ... at all.
The only up side to that statement is that its only slightly less daft sounding than the fault lies in the driveshaft.

Lets know how its resolved.

Cheers
Bob
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Old Jul 11th, 2019, 07:19   #23
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The ABS sensor has been cleaned and now the wait until the tyre pressures drop. I have tried hard braking at 40mph whilst steering and there seemed to be some ability to steer but it was not a good test as it was a dry road and brakes that are really good stop the car within a few lengths. I have noticed that the electronic stability control lights up on the dash over some really steep road humps but it may have always done that and I may just be noticing it. Apart from testing of the sensors does anyone know of a better test for the complete ABS function?
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Old Sep 22nd, 2019, 10:27   #24
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It seems that my problem has nothing to do with the AWD system but I thought that I would post a copy of the post from the thread in the V40 section just in case anyone comes looking.

Quote:
Originally Posted by SwissXC90 View Post
A 50% drop to trigger the TPMS is about right

TPMS that uses in-tyre radio transmitters are very accurate and can trigger at just a few PSI drop, as they directly measure the tyre pressure. they are not subject to distance, speed, or road geometry.

TPMS that uses wheel rotation sensors, such as yours, need a much MUCH larger drop in tyre pressure to trigger the TPMS
.…
Thanks for your input SwissXC90.

I am still waiting for a response from Volvo so I though that I would take a break from work and spend a while digging into the subject to see what I can find out, so here goes. Volvo may call them TPMS and TPM, but they are really Direct TPMS (dTPMS) and Indirect TPMS (iTPMS). I have always known that my V40 has TPM (iTPMS) and was told that it is triggered by the ESC(ABS) wheel sensor and It is based on the earlier versions of iTPMS, here is how that works. To get type approval it must be able to notice the pressure drop in one wheel before it loses 20% of pressure or 1.5bar or any four tyres after 60 minutes.

But there are flaws in the system,
and it cannot notice a slow pressure drop in both wheels on the same axle, has problems with the type of road, tyre construction, weather, etc or because the software tries to tune out false alerts, just plain doesn’t work.

Moral of the story, check your tyre pressures often and don’t bother trying to fix TPM.
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