"Random" TPMS alerts

ricketyca

Member
:
CX5
We bought the CX5 new when it was first launched in Canada. From time to time, seemingly random alerts pop up from the TPMS. On our model it is the one where there are no specific wheel sensors. The problems happen on summer or winter wheels and tires. When checked there was no appreciable difference between pressures.

My wife is the main driver, so I would just take her report, check that the pressures were about right, and reset it.
I discovered on our car, as described in the manual, we need to set the parking (emergency) brake for the reset to work. Otherwise it just seems to clear the dash light and it would come back on again once the car was driven. As long as I reset it properly, the alert did not come up for another few weeks. I thought there was a "monthly" maintenance warning that could be triggered and the service department could turn it off. However, our local guys said "not on the models sold in Canada apparently".

When riding in it together, the alert triggered and my wife said - "It almost always goes off around here". I stopped and reset it and looked around. There were several antenna masts with microwave repeaters on them.

I know many years ago with my Mazda 6 sitting in the telco's microwave beam would disable the alarm system, forcing a reset before it could be armed or disarmed, and I wondered whether someone these devices could somehow interfere with the TPMS monitoring. Thinking back, my wife was fairly sure that she has not had it trigger falsely anywhere else in our area.

So, my questions are ...
Based on their understanding of the TPMS system can anyone imagine how that could occur?
Has anyone else had spurious TPMS alerts that might tend to repeat in the same general vicinity such that they could be a similar issue?

Thanks for any thoughts. I have fashioned a hat from aluminium foil just in case!
 
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If you don't have TPMS sensors in the valve stems on each wheel the system works off of the ABS sensors. I don't see how radio interference can affect those.

If you have them in the tires warnings can get wonky when the batteries start dying.
 
As Studum says, these systems use the ABS sensors to determine wheel speed. Based on the idea that, all else being equal, an underinflated tire will roll at a different speed than one at proper pressure. Then, using computer algorithms, decide how large of a difference in speed over what length of time under what braking or acceleration conditions might indicate an inflation problem. False positives can be triggered by things like road construction/uneven pavemtent, long gradual curves, interstate highway cloverleaves where you have to make three consecutive 270 degree turns to achieve a 90 degree change of direction, etc.

High RF fields could, in theory, saturate one or more sensor inputs to the computer, but there should not be that much RF anywhere close enough to the ground to encounter vehicles (or people).
 
Thanks Rick3478 for the comments. The false positives we have seen in this location are a straight road with an 80kph (50mph) limit and minimal camber, and subsequent checks showed the tires to have equal pressure. I certainly suspect the RF in our case - especially as we had a couple of instances overseas with a car alarm system. I presume the sensors are wire connected (not wireless) and the issue would have to be an induced effect.

I mainly posted to hear comments about the possibility, and see whether there were others that with retrospect thought of an explanation for their own events.

Thanks again
 
What does pressure "about" right mean? Reset tire to a specific pressure when overnight cold, with a good digital gauge, reset the TPM and see if doing it correctly will fix it? Ed
 
Thanks Ed for your suggestion. In saying "about right" I meant that all 4 were within 1 psi of each other and the defined pressure.
 
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