TPMS, Neptune WM and Weather stations

[Dovid]

Hi all

I have been doing some testing in the last few days.

Loaded the laptop in my truck and went for a drive and I traveled about 100 meters before the TPMS data from my new winter wheels started showing up.

The pressure data was all right on but the temperature doesn't show correctly.

The program shows +54.0 F but the real temperature was -5.4 C so appears to be a bit of a mix up there. I have seen this behavior before.

 I also have a TPMS sensor in the full size spare tire that did not send any data at all. 

This spare is also a new winter wheel. The folks that work in the tire shops always tell me the TPMS will not work properly with a sensor in the spare tire. 

Those guys are wrong about a lot of things. I can install the spare and then do a relearn without a tool and without any problems. 

I also got some water meter readings along some weather station data. 

My 25 year-old weather station has all but given up so It's great to get all the weather data from the neighbors new stations that have gone up.

Cheers

 

[Alan Rothenbush]

I'm certainly no expert in these things, but tires do heat up when driven for a while, to remarkably high temperatures, in fact.  After 100 meters, maybe not so much, but after a kilometer, 60 F is an absolutely believable number, even if they started at -5 C.

[Devin Noel]

TPMS typically goes to sleep & doesn't transmit until some kind of motion sensor wakes it up as a battery saving measure. Having to drive for a few dozen seconds before it wakes up is standard behavior. That can also cause the spare tire issues. I think they wake up & beacon occasionally when in sleep mode & no rotation, which will get your spare to report eventually. But it probably varies with the different TPMS types.

Does the temperature change at all? Not all TPMS report temp. It could just be default values. If it changes it could be just an offset problem. My trailer TPMS on the RV can get pretty toasty, especially coming down the mountains with lots of breaking.

[Dovid]

Yes the temperatures reported by the sensors did rise from +54.0 F to +60.0 F, along with ambient the temperature. 

The ambient temperatures here have just risen from -30 C to  -5.0 C with ice covered roads and over a foot of recent snow cover added.

I traveled only a few miles at speeds well under 25 MPH, as road conditions are very poor, so little chance for tires to heat up.

I understand that the spare wheel would have to rotate before it would report any data to the TPMS.

 

Cheers

[Christian Z.]

The Schrader Electronics EG53MA4 was analyzed as built into Opel (OEM No. 13348393) it might be found in Saab, Opel, Vauxhall, Chevrolet best we know. What brand is your truck? Is the TPMS stock or aftermarket?

The reported number is a raw byte value (0-255), assumed to be deg F. That might be wrong or just different in your application.

Since it is a raw number (no conversion applied) you can measure at different (extreme) temperatures and derive a formula. Best case and easiest would be with a spare TPMS sensor in hand. But other people have spun their tires jacked up or e.g. mounted to a drill -- with success :)

[Dovid]

Hi Christian

The brand is Chevrolet.

I purchased 5 new sensors from my local GM dealer and paid the full price without the discount plus 11% in taxes. I got BENT.

https://www.gmcpartscanada-spg.ca/oem-parts/gm-sensor-13540600

Cheers

[Greg Troxel]

Devin Noel <devin...@gmail.com> writes:

> TPMS typically goes to sleep & doesn't transmit until some kind of motion
> sensor wakes it up as a battery saving measure. Having to drive for a few
> dozen seconds before it wakes up is standard behavior. That can also cause
> the spare tire issues. I think they wake up & beacon occasionally when in
> sleep mode & no rotation, which will get your spare to report eventually.
> But it probably varies with the different TPMS types.

Generally yes but it really varies.

Ford TPMS transmits every 6h when not driving, and often during
operation.
Toyota TPMS transmits about every 1.5 minutes when not driving. I don't
know if it's more when driving.

> Does the temperature change at all? Not all TPMS report temp. It could just
> be default values. If it changes it could be just an offset problem. My
> trailer TPMS on the RV can get pretty toasty, especially coming down the
> mountains with lots of breaking.

Driving 100m is not going to change the temp much. I don't believe even
1C.
What I see as typical is say 10C in the garage, and then go out and
drive 20 km and on return it might be 30C.

[Greg Troxel]

You may want to read the source code for the other TPMS decoders, and
use that as a clue for how temp is encoded. I worked on the Ford
decoder (more pressure than temp) and while some of it was correlation,
some of it was figuring out the pressure amount of 1 unit and offset,
guessing at what an engineer would have done once close. It might have
been 0.25 psi/count and some integer offset.

That was on an old car. New ones might be fundamentally metric (in
terms of some round-ish number of kPa per count, where 2.5 counts as
round).

This isn't an answer of course but looking at others might help in
decoding, with a sense of how it's generally done in the industry.