Flat Tyre Sensor

[saabby]

Left for work yesterday and the steering felt funny. First thing that came to mind was that I had a flat. But decided to drive on as I have a flat tyre indicator! So I drove for another 100m then decided to look around. Rear left tyre was flat (which coincidentally was the same one that went flat in my Golf GTI Mk5 after 3 months). So much for an indicator. Changed to the bicycle tyre and went straight to the tyre shop.

No nail on first inspection but a pinhole leak was discovered in the bath. Tyre shop reckon it was there from Day 1 slowly emptying out. Tyre manufacturing fault? Well, thank goodness I discovered the flat as the tyre is not easily available and they were able to fit it.

So why didn't the sensor not pick it up? Is my ABS faulty or did the $2,000 dealer delivery not include a reset of tyre sensor?

[wai]

There are two types of flat tyre indicators.

There are those that monitor the actual tyre pressure, and those that try to detect the tyre diameter either by trying to measure the tyre diameter or by measuring the rotational speed relative to the other wheels.

The only ones to absolutely trust are the ones that have actual pressure monitors that then send the reading to a dashboard or other display. The ones that try to establish the rolling diameter are not that accurate as they generally measure this at the top of the tyre. Tyres tend not to be that flat at the top, even ones with 0 tyre pressure.

Even ones that measure rotational speed relative to other can fail to detect a flat, particularly if you have ultra low profile tyres. With these tyres, if it is set too sensitive, then every time you went around a corner too fast it would trigger.

If you ever feel that there is something not quite right with your car, NEVER assume that you have technology that will take care of you. Get out and check things. Technology is very unreliable. When it works it is great, but the best control unit is the driver.

[danntsi77]

3 days after i got my car, i was on the highway when the tyre pressure monitor alert came up on the dash, i pulled over at the next safe place and on the left rear tyre was a big nail that had punctured its way into the tyre.

The system needs to be reset anytime you adjust your tyres pressures or buy brand new tyres....

This is done while holding down the button that is located in the glovebox while the ignition is in the "ON" postion until your hear a beep/dong.....

In respects to the slow leak, .......if you were say losing only 3 psi per day in air pressure via a small leak this might be within the non alert range........

Where as if you lost 10psi within the space of ten minutes from a nail punctured into the tyre then the system would recognize that as an alert.........

[gavs]

If indeed a slow leak, then it still should have been picked up regardless. I would say your second guess is the more accurate one. Because the system works off th eABS sensor (as you correctly mentioned) then regardless of how fast or how slow the leak is, if the geometry of the wheel position has altered, then the sensor will pick it up when it gets out of the tolerance range.

[blutopless2]

I have the tpms in my jetta and it has worked well since day one. It picks up a difference of about 6 PSI in the tyre going flat.
as said above the system needs to be reset every time you make any alterations to tyre pressures or new tyres etc to keep it working correctly.
If you think there is a fault with your tpms then get it checked by VW or do a road test yourself by setting all pressures the same, resetting the system then dropping one tyre down by about 6-7psi and drive the car... this should be enough to activate the warning.