# TPMS reading wrong pressure



## larry_ok (Jun 15, 2015)

Hey all. Here's the back story.

I have a '14 ECO and when I bought it, the dealer swapped out the tire air for nitrogen, as part of the ECO package. Now that I have moved, the dealer here does not have a nitrogen machine, but I did find a tire shop that offers lifetime nitrogen for $25.

Here's the problem.

The on-board TPMS says my L/R is at 26 pounds. The nitrogen machine at the tire shop shows all 4 tires at 35 pounds. Is this something that the dealer needs to look at and would it be under warranty?

Thanks,
Larry


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## ChevyGuy (Dec 13, 2014)

Since it's just one tire, it does sound like a sensor issue. (I'm assuming you don't have a full-sized spare tire - otherwise I'd suggest you check the spare to make sure that's not where the reading is coming from.)

One caution - a non-GM approved tire sealant could gunk things up. In that case it's not going to be covered by any warranty. Otherwise, assuming you haven't gone over the 36,000 mile limit for B2B, I'd think it would be covered.


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## newsguy99 (May 24, 2013)

have them reset the TPMS for you.. That should clear everything up.


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## larry_ok (Jun 15, 2015)

Thanks guys. No tire sealant and no other mods since purchasing new last year. I will take it in this coming week and have them look at it.

Thanks again,
Larry


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## ChevyGuy (Dec 13, 2014)

newsguy99 said:


> have them reset the TPMS for you.. That should clear everything up.


I don't think the reset resets the calibration. The computer might be confused as to which sensor is the L/R, but that sensor has to be in range to get a reading. But he says all his tires are fine.


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## obermd (Mar 3, 2012)

I second the "bad" sensor in one tire. As long as you are under the B2B warranty and still have the OEM tires this should be covered. By the way, spend the $25 on an air pump - nitrogen in passenger car tires has no benefits.


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## spacedout (Dec 7, 2010)

Don't waste your money on nitrogen in your tires. If its free fine then but since it does nothing at all its not something you should spend your money on. Had nitrogen in my last set of tires and saw no difference at all in MPG, tire also still gained PSI as the tire warmed.


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## NickD (Dec 10, 2011)

Key advantage of nitrogen is getting dry air, but already have a moisture filter on my air compressor, close enough. Is required on large aircraft, but dealing with around 350 psi pressures with aircraft that fly in way subzero temperatures.

How in the world did I get by with driving vehicles using compressed air and without TPMS for some odd 60 years? Heard some got by, by deflating the tire to reset the TPMS. But wouldn't dare do this with the tire on the ground, could break your beads, better jack it up first. Or get a second mortgage on your home and purchase that electronic whatever. 

Properly working TPMS does give you knowledge, but not a cure. Ha, in talking to one of my kids on this issue, only place they can find air is at a tire dealer or your car dealer that maintains bankers hours. And don't even do this for free, one kid had to pay for this.

Could buy something like this:










That operates off your cigar lighter socket, but don't trust that Made in China gauge, buy a good gauge. Ha, also allow a half a day to fill a tire.

DIY? Cost around 30 bucks for one of these.










Can still break a bead with a hydraulic jack under the bumper of my motorhome, but also need rim sealer. Heard a dealer charges 80 bucks per tire, times four, with tax comes to 340 bucks that use to cost a couple of bucks to get done. 

Think they want us to trade our cars in before the BB warranty expires. 

Could always check your tires with a gague, only thing TPMS does is let you do this in the car to save you about 120 seconds worth of work. But is the law!!!


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## Vetterin (Mar 27, 2011)

Remember...you already have 78% nitrogen in your car tires if you use.................AIR so what's the point? Now if you drive an airplane that's another story.


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## ChevyGuy (Dec 13, 2014)

NickD said:


> Or get a second mortgage on your home and purchase that electronic whatever.


I'm surprised no one have figured out how to build one. IIRC, it's a magnetic field at some low frequency. (150Khz?) It's not rocket science. Heck, got a grid dip meter? You may already have a TPMS reset device.


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## larry_ok (Jun 15, 2015)

Turns out when they rotated the tires, they did not reset the TPMS. They reset and re-calibrated it for me, problem solved. Thanks for the advice guys.


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## ChevyGuy (Dec 13, 2014)

So, was the low tire a full-sized spare? That's the only way I can see that fixing a low tire. Or maybe your winter tires you store in the garage?


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## ChevyMgr (Oct 27, 2010)

Resetting the sensors with a reset tool fixes these type of issues often.


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## ChevyGuy (Dec 13, 2014)

ChevyMgr said:


> Resetting the sensors with a reset tool fixes these type of issues often.


Can you enlighten me as to why that would fix a low pressure reading? Reading a wrong tire, I can understand.


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## Robby (Mar 1, 2013)

ChevyGuy said:


> Can you enlighten me as to why that would fix a low pressure reading? Reading a wrong tire, I can understand.


Although I am not ChevyMgr, I can tell you that a relearn will often re-align the sensor with the actual tire pressure.
I've done it on my Malibu as well as the Cruze.......the dash readout won't agree with the actual gauge pressure, I use the re-learn tool, and now the gauge and dash readout agree.

As far as why????? I can't even speculate why the sensor falls out of range....but evidently they do.....my dealer agrees...says this is rather common and, no, no answers from Chevrolet.

I've concluded it falls under the 'Blue Whale Theory' ie 'Thats just the way it farging is' and won't frett....got enouph useless flotsam stuck in my head as it is.

Rob


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## larry_ok (Jun 15, 2015)

ChevyGuy said:


> So, was the low tire a full-sized spare? That's the only way I can see that fixing a low tire. Or maybe your winter tires you store in the garage?


No, the spare is a doughnut and was at correct pressure. Once he reset and re-calibrated the TPMS, everything was fine. All tires were at correct pressure.


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## ChevyGuy (Dec 13, 2014)

Robby said:


> Although I am not ChevyMgr, I can tell you that a relearn will often re-align the sensor with the actual tire pressure.
> I've done it on my Malibu as well as the Cruze.......the dash readout won't agree with the actual gauge pressure, I use the re-learn tool, and now the gauge and dash readout agree.


Interesting. Suddenly my desire to get a reset device increased. But I'm too cheap to buy one, so I may hack one together. 

I wouldn't think the pressure sensor itself could reset without getting a 0 PSI reference. So I think it has to be a quirk in the electronics.


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## Robby (Mar 1, 2013)

ChevyGuy said:


> Interesting. Suddenly my desire to get a reset device increased. But I'm too cheap to buy one, so I may hack one together.
> 
> I wouldn't think the pressure sensor itself could reset without getting a 0 PSI reference. So I think it has to be a quirk in the electronics.


You are forcing me to think a bit.

Keep in mind each wheel sensor is actually a radio transmitter/reciever with a pressure sensor operating at 350 mhz.
The car also has a transciever that memorizes each sensors specific ID# and its current position.

Since it is a radio based system, and we live in a world of radio waves using the entire spectrum of frequencies, it stands to reason that certain situations can create a signal that the cars transciever 'see's' and interpets as a sensor signal.
The re-learn tool 'wakes up' each wheel sensor so it will broadcast current pressure and the transciever then remembers the position of the sensor X4......or on some cars, the spare is monitered as well......not found on any GM to my knowledge.

Some much for WAG's but thats the best I can come up with.

Rob


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## ChevyMgr (Oct 27, 2010)

ChevyGuy said:


> Can you enlighten me as to why that would fix a low pressure reading? Reading a wrong tire, I can understand.


Why does it fix these issues? I don't know. But if I can reset tires on the service drive after other shops have rotated/tires replaced/nitro added, and it fixes the issue, I don't care why it does, just that it does. I am not an engineer and I don't dwell on why the new electronics work the way they do.

If a vehicle comes in with numerous electrical issues and a global reset will fix it. Then so be it. Don't care why, it's fixed and now it's time to go on to the next vehicle.

It's the same as my PC running slow and I reboot it. It fixes the problem so it's all good.


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## ChevyGuy (Dec 13, 2014)

ChevyMgr said:


> Why does it fix these issues? I don't know. But if I can reset tires on the service drive after other shops have rotated/tires replaced/nitro added, and it fixes the issue, I don't care why it does, just that it does. I am not an engineer and I don't dwell on why the new electronics work the way they do.


I'm not going to argue with success (I've been around long enough to know truly strange things happen), but I am an engineer and a computer geek to boot. While I don't worry about the other examples you give, the TPMS is simple enough that it should be understandable. (And strange things are interesting.)






Robby said:


> You are forcing me to think a bit.
> 
> Keep in mind each wheel sensor is actually a radio transmitter/reciever with a pressure sensor operating at 350 mhz.
> The car also has a transciever that memorizes each sensors specific ID# and its current position.
> ...


Yeah, not that complex - so how does it come up with a wrong pressure? The best theory I can come up with is that there may be more than one TPMS model (perhaps for different pressure ranges) and the receiver has forgotten which one it is, so it's applying the wrong translation table. But that's a total WAG without any facts in evidence. So I'll just start a rumor that it's a bug caused by the NSA installing tracking software. :laugh:



Robby said:


> Since it is a radio based system, and we live in a world of radio waves using the entire spectrum of frequencies, it stands to reason that certain situations can create a signal that the cars transciever 'see's' and interpets as a sensor signal.


I'd think that would be a transient problem and would correct itself the next time the TPMS transmits.


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## KENSTV123 (Sep 21, 2014)

It may be that the sensor is locked up and not calling home and the receiver is just retaining last read or last erroneous read, there is a TINY microprocessor inside the TPMS sensor and it is subject to lockup, using the re-learn tool causes a reset of the micro and handshake with receiver is reestablished, if you do a total microprocessor count in the cruze I'm sure it's over 20 !!!


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## ChevyGuy (Dec 13, 2014)

KENSTV123 said:


> It may be that the sensor is locked up and not calling home and the receiver is just retaining last read or last erroneous read,


I'm pretty sure that if the unit fails to call home, the display shows "--" for the pressure and the light comes on. That's a system malfunction.

I suppose it could happen that the processor locks onto an old reading, but those are such simple processors with such a simple task, I'm not sure why they would lock up.

But the test there would be to see if simply using the relearn tool without putting the car into relearn mode fixes it.


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