Forum Discussion

Talldog's avatar
Talldog
Explorer
Sep 26, 2017

Do TST 507 sensors just go bad?

I had brand new tires and the TST 507 installed on my motorhome this past spring, and everything has been working fine until the end of Labor Day weekend. I keep all of my tires at 120psi, but when I fired up the MH to come home, one of the tires was reading 110. No problem coming home, but this past Sunday was the first time I've had to look at it, and the tire was now reading 106, a loss of 4psi in less than 3 weeks. Once I pulled the sensor, 2 different stick gauges showed the pressure at 110, so the sensor was reading 4psi low, which it wasn't doing previously. I inflated the tire to 120 and put the sensor back on, and it was reading 116.

Today when I started up the MH, the sensor was reading 115, and when I checked with the gauges, they were reading 119, so it lost 1psi in 2 days. At this point, I don't know whether it's the tire or the sensor, so I left the sensor off and put a valve stem cap on. I'll check it again in a couple of days to see whether it's lost any more air.

I'm wondering though, can a sensor that's only a few months old and has been working fine just start leaking? It had never been removed from the tire before Sunday. Also, what's up with it suddenly reading 4psi low? It just seems like something might be wrong with the sensor.
  • Dutch_12078's avatar
    Dutch_12078
    Explorer II
    Sep 27, 2017
    fj12ryder wrote:
    FWIW my TST sensors all measure with 1-2 psi of the readings I get with a gauge.

    Same here, all 10 TST sensors are within plus or minus a pound of my verified gauge readings.
  • fj12ryder's avatar
    fj12ryder
    Explorer III
    Sep 27, 2017
    FWIW my TST sensors all measure with 1-2 psi of the readings I get with a gauge.

    I take the sensors off my triple axle every fall and put them back on in the spring. I have had to replace 2 batteries out of six sensors and those were shortly after I got the system. I bought it a little over 4 years ago.
  • RCMAN46's avatar
    RCMAN46
    Explorer
    Sep 27, 2017
    " Their suggestion was to loosen the valve core in case it was not fully engaging with the sensor, which doesn't make sense to me."

    I have seen this suggestion from several TPMS manufacturers.

    Actually once the sensor is installed the valve core no longer has to seal as the TPMS depresses the valve core.

    So if the valve core has been loosened to the point it has a little leakage the TPMS sensor will still work as the sensor will seal the valve stem.

    I fill my tires about 2 psi above desired pressure. Then by the time the sensor is installed I get close to desired pressure from the TPMS.

    What I try to do is get all 4 TPMS sensors reporting the same pressure. Pressures from a given tire that does not match the other tires is what I am mostly concerned with.

    If a tire is 5 psi or more different than the others that tire most likely has a problem and should be checked ASAP.
  • Talldog's avatar
    Talldog
    Explorer
    Sep 27, 2017
    Horizons28 wrote:
    TST customer service is very good, give them a call.

    I've already called them. They made the point about the pressure reading not necessarily being spot on, but it doesn't make sense to me that it would be accurate for 4 months and then out of the blue start reading 4psi low. They also didn't think it would start leaking so soon, especially since it had never been removed. Their suggestion was to loosen the valve core in case it was not fully engaging with the sensor, which doesn't make sense to me.
  • Dutch_12078's avatar
    Dutch_12078
    Explorer II
    Sep 27, 2017
    ScottG wrote:
    I'm curious, do the sensors have batteries in them or are they the newest type without batts?
    If they are the latter, the wheels have to spin a while before accurate readings are given.

    Unless TST has something new out that's not on their website yet, they do not have a "batteryless" sensor available. The user replaceable (model 507) and 5-year (model 510) battery sensors are the only one listed.
  • Horizons28's avatar
    Horizons28
    Explorer
    Sep 27, 2017
    I find you can't really use those sensors as an accurate measure of tire pressure. I'll top off my tires and, though the gauge shows they are all 80, the TPMS sensors will show 78-82. If you suspect a leak there is a rubber o-ring inside. The company will send you a free package of replacements. The rings will degrade over time, especially as I take mine off and on as I put my unit in and out of storage. I have had sensors fail completely- it will display nothing at that point. TST customer service is very good, give them a call.
  • Talldog's avatar
    Talldog
    Explorer
    Sep 27, 2017
    ScottG wrote:
    I'm curious, do the sensors have batteries in them or are they the newest type without batts?

    They're the ones with batteries.
  • Harvey51's avatar
    Harvey51
    Explorer
    Sep 27, 2017
    Hmm, I've been noticing pressures dropping slightly lately. Could it be temperature?
    Pressure in a closed container is proportional to Absolute temperature, so a 5 degree Celsius drop from 300 A (27C or 80F) would cause 110 psi to diminish by 5/300*110 = 1.8 psi.
  • fj12ryder's avatar
    fj12ryder
    Explorer III
    Sep 27, 2017
    It's possible the battery is bad. I'd switch it around and see if it works on another tire. If it's the flow through sensor there could be an issue with the sensor not reading pressure correctly, and it may be time for a new sensor.
  • ScottG's avatar
    ScottG
    Nomad
    Sep 27, 2017
    I'm curious, do the sensors have batteries in them or are they the newest type without batts?
    If they are the latter, the wheels have to spin a while before accurate readings are given.

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