Erroneous low tire pressure warning?

katmar

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16 CX-5 GT and 13 CX-5 Touring AWD
The low tire pressure warning light (and beep) popped on the other morning on my 2013 CX-5 Touring.

I stopped and checked all four tires, and all were 32.0 or 32.5 psi. I reset the warning, and it hasn't come back in the days since then.

Has that happened to anyone else?

It happened about 2 miles into my morning commute. The tires and wheels hadn't been touched or modified in any way, ordinary day, ordinary road, no tire slippage or anything. It was a bit colder than the usual, but I didn't think our CX-5's measured actual air pressure anymore, but rather the rotational speed difference between tires... so I don't think that would matter?
 
I've had mine go off multiple times. Each time it went off I took it to the dealership (it's halfway between work and home) and they said there's nothing wrong and reset it. It actually just went off yesterday while my wife was driving and again it's bogus.
 
Has the temperature changed drastically the last few days or when the low pressure warning light comes on?
Usually if it's in the 90s & then temps drop to the 60s, the tire pressure drops. It's 1 psi per 10 deg F.
 
Has the temperature changed drastically the last few days or when the low pressure warning light comes on?
Usually if it's in the 90s & then temps drop to the 60s, the tire pressure drops. It's 1 psi per 10 deg F.

It was an unusually chilly morning when mine went off, though I'm not sure if that affects the CX-5's sensors? My RX-8 used to alarm on the first really cold morning of winter, as it measured actual tire pressure.

But it was my understanding that the CX-5 just measures rotation speed differences between the tires, and so in theory if all four tires to drop to 10 psi... would it even warn us?
 
It was an unusually chilly morning when mine went off, though I'm not sure if that affects the CX-5's sensors? My RX-8 used to alarm on the first really cold morning of winter, as it measured actual tire pressure.

But it was my understanding that the CX-5 just measures rotation speed differences between the tires, and so in theory if all four tires to drop to 10 psi... would it even warn us?
Yes it would if you reset the TPMS after you filled the tires at 36psi.
The warning goes off when it measures a drop in tire pressure when the rotations increase due to lower diameter of the tire(s).
Let's say you filled the tires to 25psi or reset the TPMS when the tires were at 25psi, the system would not warn you.
That is why the owners manual tells you to rest it every time you fill the tires.
Otherwise, the system is taking your last reset as the 'optimal' tire pressure.
 
But it was my understanding that the CX-5 just measures rotation speed differences between the tires, and so in theory if all four tires to drop to 10 psi... would it even warn us?


No, I can't imagine how it would know the difference (short of having an on-board radar to measure actual vehicle speed).
 
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Yes it would if you reset the TPMS after you filled the tires at 36psi.
The warning goes off when it measures a drop in tire pressure when the rotations increase due to lower diameter of the tire(s).
Let's say you filled the tires to 25psi or reset the TPMS when the tires were at 25psi, the system would not warn you.
That is why the owners manual tells you to rest it every time you fill the tires.
Otherwise, the system is taking your last reset as the 'optimal' tire pressure.

Actually it can only detect differences in the rotation between the different tires. If you start at 36 and then they all get reduced to 31 it won't go off since they are all spinning the same amount. Because as Mike pointed out it has no master reference for how fast the vehicle is actually going to compare the rotations of all 4 tires.

If all 4 tires are spinning .1% faster than usual to go 45 mph it won't know. It can only tell when one or more tires are spinning faster than the others.

I'm curious what the reset button does. Does it allow for different tread depth by taking a reading of the different wheel speeds right after it is reset?
 
Actually it can only detect differences in the rotation between the different tires. If you start at 36 and then they all get reduced to 31 it won't go off since they are all spinning the same amount. Because as Mike pointed out it has no master reference for how fast the vehicle is actually going to compare the rotations of all 4 tires.

If all 4 tires are spinning .1% faster than usual to go 45 mph it won't know. It can only tell when one or more tires are spinning faster than the others.

I'm curious what the reset button does. Does it allow for different tread depth by taking a reading of the different wheel speeds right after it is reset?
You're right.
This is from the owners manual.
NOTE
l Perform tire pressure adjustment when the tires are cold. Tire pressure will vary according to the tire temperature, therefore let the vehicle stand for 1 hour or only drive it 1.6 km (1 mile) or less before adjusting the tire pressures. When pressure is adjusted on hot tires to the cold inflation pressure, the TPMS warning light/beep may turn on after the tires cool and pressure drops below specification.
Also, an illuminated TPMS warning light, resulting from the tire air pressure dropping due to cold ambient temperature will remain illuminated even if the ambient temperature rises. In this case, it will also be necessary to adjust the tire air pressures. If the TPMS warning light illuminates due to a drop in tire air pressure, make sure to check and adjust the tire air pressures.
l Tires lose air naturally over time and the TPMS cannot tell if the tires are getting too soft over time or you have a flat. However, when you find one low tire in a set of four- that is an indication of trouble; you should have someone drive the vehicle slowly forward so you can inspect any low tire for cuts and any metal objects sticking through tread or sidewall. Put a few drops of water in the valve stem to see if it bubbles indicating a bad valve. Leaks need to be addressed by more than simply refilling the trouble tire as leaks are dangerous - take it to an Authorized Mazda Dealer.
 
Yeah. So, what are the chances that all four tires will lose air at a rate so similar with one another, that the ECU won't pick up on a rotational difference of .1%?
The system ought to do its job, if there is trouble. If you're expecting it to do a job or perform a maintenance item that you should be doing periodically...well, you can't fix stupid.

Having said that, this particular design will inherently result in erroneous TPMS alarms. You should expect it to happen from time to time.
 
Having said that, this particular design will inherently result in erroneous TPMS alarms. You should expect it to happen from time to time.

I agree that you can't fix stupid.

Disagree that false alarms can be expected to be a regular event. After more than 10,000 miles and having gone from summer at sea level to winter at 5,000 feet and everything in between, all I've ever needed to do was a TPMS reset (push of a button) after switching from summer to winter tires and accurately setting the pressure (before pushing the button). I think false alarms are caused by pushing the TPMS reset button when the tires are not equalized properly or running tires that are defective (meaning they are mismatched and heat up and build pressure differently from tire to tire).
 
My alarm has yet to set off, in fact I'm not totally sure it even works.
When I first got the car I increased all the pressures to 38 psi all round, no alarm sounded?
 
My alarm has yet to set off, in fact I'm not totally sure it even works.
When I first got the car I increased all the pressures to 38 psi all round, no alarm sounded?

Has to be at least 10% difference before it will set off.
 
The thing I always forget is to reset the reminder to check the tyres. My reminder came on the other day, I thought I had a problem. I checked all the tyres and they were fine....then I remembered to reset the reminder and it switched off. doh!
 
The thing I always forget is to reset the reminder to check the tyres. My reminder came on the other day, I thought I had a problem. I checked all the tyres and they were fine....then I remembered to reset the reminder and it switched off. doh!
I turned off the reminder bc of this. Wife thought there was a flat or something wrong every time the reminder came on.
If I was the primary driver, then I'd use the reminder.
 
yes.. my wife got a false alarm today on the freeway coming home from work. our CX5 is only a month old. tire pressures were 39/39/38.5/38.5... guess ill reset it.
 
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