My Greenline II is fitted with the tyre pressure monitor and I was wondering how accurate/ good the system is.

Yesterday I checked my tyre pressures to find that three of the tyres were a full bar down and one was nearly a full bar.

I would expect the system to have come on after only a small loss of pressure say .4 bar.

It only works on wheel speed so if all are low without one being a lot lower than the rest it won't indicate a problem.

Got caught out like that on our passat, if they all go down at the same rate it will not pick it up.

It has picked up two slow punctures though.

So i catches the tyres if there is a big drop all of a sudden, but not a very slow loss of pressure ? Surely its set at a pressure range and beeps if they go below ?

The cheaper version, works off the abs system, if the rolling circumfrence changes sigificantly between the wheels it alarms. I have read on us forums it can be retrofitted to the passat by buying the switch and putting the code in the ecu.

Just done all the tyre pressures on my VRS, turns out they were all a bit low.

I did 2.5 bar front and 2.4 bar rear and then set the Tyre Pressure Monitor, so it will be interesting to see if it does detect anything (touch wood I don't get any punctures in the first place!)

So i catches the tyres if there is a big drop all of a sudden, but not a very slow loss of pressure ? Surely its set at a pressure range and beeps if they go below ?

Tyre pressures dont come into it, it does not monitor the actual tyre pressures at all. What it does do is monitor the rotation of all the wheels, as a tyre loses pressure the wheel needs to rotate faster to cover the same ground a fully inflated one. The TPM system picks up this difference and alerts you of a slow puncture. If all the tyres lose air at the same rate then the system will assume nothing is wrong because the wheel rotation rate remains the same.

Thanks Manny.

Interesting.

Thanks for the replies.

The manual states " The tyre pressure monitoring system compares with the aid of the ABS sensors the

speed and also the rolling circumference of the individual wheels. If the tyre inflation

pressure is significantly changed and thus the rolling circumference of a wheel, Basic setting of the system

After changing the tyre inflation pressures or after changing one or several wheels, a

basic setting of the system must be carried out as follows.

• Inflate all tyres to the specified inflation pressure
  
• Switch on the ignition.
  
• Press button for more than 2 seconds. While pressing the button, the warning light lights up.
  

At the same time the basic values are stored, which is confirmed with an acoustic sound and then the warning light goes out.

Functional description

After the basic setting of the system the “adaptation” of the tyre inflation pressures and then the tyre pressure control in the individual tyres are performed.

Warning light lights up If the tyre inflation pressure of at least one wheel is insufficiently inflated in comparison to the stored basic value, if the warning light lights up. Inflate all tyres to the specified inflation pressure, and then perform a basic setting of the system.

These insructions leave me to belive the system should have told me the tyres were deflated compared to each tyres stored value.

The manual then goes on to say "The tyre pressure monitoring system: does not replace the regular tyre inflation pressure control, because the system cannot detect an even pressure loss."

So I have come to the decision the TPM might as well not be installed - with regular pressure checks you are likley to identify a slow puncture before the system.

Thanks again for that. Appreciate the full story on the system.

I had a double near side blow with no indication, so it was a crap system for me.

To be fair to the car, It felt fine on the road.....

Did a test yesterday and deflated one tyre to 1bar below recommended pressure then went for a short drive.

And yes, no the TPM warning light did not come on :S. Have I got a faulty system?

It doesn't tell you which tyre is deflated?