Tire Pressure Monitoring System Experience?

[mbsl98]

The '07 XC70 has a tire pressure monitoring system as standard. Is this new this year, or do some of you have this on earlier years? Apparently, it operates through tire pressure transmitters mounted in the tire stems, not by measuring tire rotation. Therefore, you need to acquire more of these special valve stems if you want to use separate winter tires, or you will get tire pressure warnings all the time.

I was interested in getting a full size fifth wheel and tire to add to the rotation, if it will fit in the tire well (haven't tested that yet) - would give me a perfectly matching spare as well as a back-up replacement if I destroy a tire along teh way. My question now is what effect this tire monitoring system will have - if I add special transmitter, I will have five transmitters running, but does computer deal with this, or get confused if it only expects to read four sensors at a time?

Also, any info on how these transmitters get powered to send a signal? If they are in the tire valve, no battery or electric's.

[Lynn Brockman]

Hi, Mike - I looked at this system, and it looks like while the sensor and the valve stem are one unit, it is not likely that you would need to replace them unless they got damaged by impact or by a careless tire installer. I cannot see that there are batteries separately listed for them, so I am guessing that they operate through kinetic power, and maybe an internal (rechargable) battery. They speak to the car on either 315 or 443MHz radio frequency picked up by an antenna somewhere on the car. I think (but don't know for certain) that while they each transmit their own pressure information, the pressure notification probably won't be tripped except where a substantial enough pressure differential exists between one tire and the other 3. In any case, you should probably be able to buy a full size spare wheel with the same size tire and install a sensor on the wheel as with the others. If a different tire pressure is needed for the winter tires and the pressure is outside of Volvo's normal pressure range, I'm sure this should be programmable by Volvo service.

Hopefully this helps :-)

- Lynn

[mbsl98]

Thanks. I have found out that the pressure transmitters in tire valves transmit info from about 20 MPH and above, so there must be some form of energy related to rotation. If so, a fifth wheel sensor should be dormant and not a problem. It will be interesting to see how much a second set of sensors will ad to teh snow tire bill :-).