TPMS Strange Reading ...

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afchap

afchap

Well-known member
Joined
Dec 19, 2008
Posts
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...East TX, or on the road...
Recently my Tire Traker TPMS alarmed, indicating a leaking tire. It showed the front right toad tire at 31psi, 134 degrees.  Checked the left, at 37psi, 112 degrees. Outside temp apx 106 degrees. Cold psi should be 35.

The right front normally runs considerably hotter than the left, presumably because of hot diesel exhaust dumping right in front of it, so 134 degrees was not really unusual but the 31 psi did concern me just a little. There was no place to pull over so I kept an eye on the tire, readings did not change. 

Apx 10 miles later I found a place to pull over. I took the TPMS monitor with me outside to check the tire and realized it was no longer alarming. The tire reading were now 36 psi, 114 degrees. The tire checked normal. We continued the trip with no other alarms.
 
I had a similar thing happen with my Pressure Pro TPMS 3-4 years ago, it has not repeated. 

Suggestion, any time you have reading out of spec take your manual pressure gauge and check the pressure. 
 
All these devices are radios,  the sensors are trransmitters and the display a receiver.

A "Strange" reading that vanishes.. It might be another TPMS equipped vehicle where the sensor sends the same ID,, or it could be radio frequency interference from a nearby device (IE: Vehicle ignition system, competing system, CB or other transmitter).
 
What John says.  These are low-grade radios and the transmission protocol probably lacks much in the way of error checking, source validation, and other methods of integrity checking. Not even up to internet standards, and those aren't very high either.

A single bit dropped or inverted in a transmission, or a stray signal from another source (not necessarily even another TPMS) could fool the receiver into signally an alarm or simply display erroneous data. There are a zillion radio signals in the air these days, so false or erroneous packets of digital info are a real possibility. The better systems take measures to prevent that (it's part of the transmission "protocol"), single purpose, short range, consumer-grade gadgets often do little. We ain't talking mil-spec communications!
 
One thing to remember the sensors on most TPMS systems send a single signal pulse about every 5 minutes.  Only sudden pressure loss will result in signal transmission in less than 5 minutes.  This can be as much as 15 seconds on sudden pressure loss.

So if one signal pulse has been compromised you will see that pressure for about 5 minutes.

But if you have a TST system and the error was a result of a weak signal the TST will display that reading for as long as an hour before it reports a loss of signal.

What I am trying to explain if you get at least one signal from a sensor within one hour the TST system will not report a loss of signal.
 
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