Automotive TPMS - DIY?

[paulca]

So my new car has TPMS - Tyre Pressure Monitoring System

This is great, if you get a slow puncture (or a fast one) it will light a warning light to tell you one of your tyres is under pressure.

The problem is I have two sets of wheels.  Summer and Winter.  The summer's have the factory fitted sensors.  The winters have none.

Of course after driving for 15 minutes on the winters the TPMS gave up on finding the sensors and now permanently displays the tyre pressure warning.

There are a number of options available to me:
1.  Ignore the warning light, try not to let it bug me (Difficult)
2.  Get the dealership to put sensors in the winters and charge me for an ECU "relearn"  and redo it again in summer.  Loads-a-money
3.  Buy programmable sensors and get a tyre place to read the codes off the summers and appy them to the winters. (size-able-money)
4.  Buy the reader and programmer myself to do it. (loads-a-money)
5.  There has to be an easier way.

So I thought I would ask here where they are many a knowledgeable person if this TPMS protocol is easy to hack without buying the expensive kit.  The cheapest universal reader I can find here in the UK is like £130.  Same again for the programmer or a kit of circa £250.  There are cheap chinese devices for £35 but as they don't even have a display or any kind of instructions I can't even tell what they do exactly.

A local garage will charge me around £160 for 4 sensors and the cloning and fitting.  This should only need done once, at least until the batteries run out which won't be for 5-7 years or so.  The most annoying thing about this is, I'll need to load the summer tyres into the car and take them to the garage so they can read them.  Faff.

Of course I will still need a tyre place to fit the sensors, but that shouldn't cost more than £30-40 to refit 4 tyres.

[firewalker]

Check if you can disable the tpms on demand with an easy way.

Alexander.

[G7PSK]

Get a cheap can bus reader and cancel the codes, TMS is most likely a hazard anyway as you get reliant on it and don't check the tyres there are other problems with tyres other than pressure and the TMS is most likely not accurate anyway.

[AndyC_772]

Do you have run-flat tyres?

I do. A couple of years ago I was on my way to see a customer when there was a 'ping' and a warning message came up on my car's screen saying I had a flat tyre.

I pulled over to check, and sure enough, it was flat as a pancake.

Thing is, other than the message from the TPMS, I had no idea. Maybe the steering pulled slightly to one side, but no more so than usual on a cambered road surface. The run-flat tyre was brilliant; I completed my customer visit without even having to change a wheel, although I did make myself unpopular driving home below 50mph.

Without the TPMS I'd probably have driven further and faster, which could have ended badly. Please think carefully before turning it off.

[paulca]

Disabling the TPMS cannot be done with ODBII/Canbus, not even with the official dealership diagnostics software (Toyota TechStream).  This is apparently due to legislation saying that all new cars must have TPMS fitted and functional, so Toyota cannot legally allow you to disable it.

The only option is to take the dash apart and remove/cover the bulb.

I'm currently leaning towards the "ignore the light" for 4-5 months a year.

The MOT is not until July (in 3 years time), but a TPMS warning light will fail an MOT.  Thankfully my summer tyres will be on the car and so the system will be functioning.

EDIT:  What *can* be done with the Tech Stream software is input new codes for the TPMS.  So in theory I could buy 4 basic sensors with the right freuency, having them fitted to the winters and reprogram the TPMS myself twice a year.

The downside is the TechStream software allows fairly low level access into the ECU and I would be slightly concerned I could brick the ECU or break stuff I'd need the dealership to fix at huge cost.

[paulca]

Awww booo.

Someone on another forum just burst my bubble.  They proposed that should I have an accident the insurance company could potentially argue some reduced liability to pay out as I have an inoperable but legally required safety system, the TPMS.  So leaving the light illuminated does carry it's legal risks.

Also, it seems the TechStream software may or may not work depending on which bus cable you buy.  There are varied reports of some working and some not working.  Some let you view but the software goes into read-only mode as it doesn't like the cable when you try and write.  This might just be cheap chinese knock-off cables, I need to research further.

[CJay]

[labjr]

I'm assuming your new vehicle is a Toyota?

I've used Techstream to program new TPMS sensor ID's in my 2007 Camry. There has to be four sensors programmed at all times for the light to go off.

Some people make a pressure chamber out of PVC pipe or other material, put four TPMS sensors and pressurize it. Then program the sensors into the vehicle and leave it your car so it fools the system.

I will say though, the system has saved me a couple of times.

[glarsson]

There are a number of options available to me:
1.  Ignore the warning light, try not to let it bug me (Difficult)
2.  Get the dealership to put sensors in the winters and charge me for an ECU "relearn"  and redo it again in summer.  Loads-a-money
3.  Buy programmable sensors and get a tyre place to read the codes off the summers and appy them to the winters. (size-able-money)
4.  Buy the reader and programmer myself to do it. (loads-a-money)
5.  There has to be an easier way.

6.  Return car as it is not fit for purpose.

This TMPS system is so badly implemented that it would be a deal breaker for me.
The TMPS system in my car identifies the sensors by itself. It remembers summer and winter wheels and switches immediately between them, but if I buy new sensors or switches the tires around then I have to drive a few km for the new sensors to be recognized and remembered. This means that a working and practical TMPS system can be designed, built and delivered. The system in your car is just broken as designed. 

[labjr]

Well newer systems are better. My Toyota is 11 years old.

[glarsson]

Well newer systems are better. My Toyota is 11 years old.

Mine (obviously not a Toyota) was manufactured in late 2010, but this particular TPMS system was introduced in 2008 (as far as I know).
Several modern TPMS systems are still broken by design.

[floobydust]

TPMS is a ripoff, I wish it was open but we all know some asshole hacker would wreck them at the mall parking lot and then encryption is needed 

Toyota body-ECU cannot hold two sets of tires (summer/winter) so pay $50 twice a year to reprogram TPMS.
You have to RF read each wheel ID, then CANBUS to program the body-ECU. The "button" does FA.

There's complications because the tire pressure is known, so a front/rear swap gets dangerous because the alarm pressure limits are then wrong. I haven't figured out where that data is stored.

Only a few companies make TPMS readers and OBD programmers, for hundreds of dollars.
So you pay almost the price of a tire every year to reprogram this crap.

[paulca]

floobydust, exactly.  Although the button in my car resets the nominal tyre pressure when you change tyre pressure.  So if for example you dropped the tyre pressures from 38PSI to 33PSI the light doesn't come on when you drive off.  Mine does not determine which wheel is which and as the car has a near 50/50 balance all tyres go to the same pressure anyway.  It does support a range of 30-38PSI though.

I've run the whole winter with the light on.  It's only slightly annoying.  Mostly that is doesn't come on for about 15 minutes, then it flashes at me for at least a minute which is distracting before just remaining on.

Winter tyres are due to come off anyway when I get time.

[orion242]

TPMS is a ripoff, I wish it was open but we all know some asshole hacker would wreck them at the mall parking lot

They must be somewhat open as I read companies use these to track you as you drive about.  Your car sending out unique identifiers every so often for anyone listening.

electrical tape over the light.  problem solved.

[paulca]

TPMS is a ripoff, I wish it was open but we all know some asshole hacker would wreck them at the mall parking lot

They must be somewhat open as I read companies use these to track you as you drive about.  Your car sending out unique identifiers every so often for anyone listening.

electrical tape over the light.  problem solved.

Unfortunately they are now a legal requirement in the UK on all new cars.  If it's fitted, it must be working.  The MOT test requires the tester to verify the light comes on when the ignition is switched on and goes off again correctly.  A fault indication will fail the MOT.

[floobydust]

It seems wireless hackers seek fame and glory attacking TPMS, more than us poor engineers trying to thwart the car dealership/tire shops ripping people off.
I think it's a huge industry over something touted to improve safety, yet it's not on semi trucks and confusing to installers and customers, and ultimately costs more than the tire itself.

It's better to track people using their Bluetooth ID's- from their phone, car entertainment system etc. which is something my municipality is doing to "monitor traffic flow". They have Bluetooth ID harvesters mounted on poles along the freeways, to see where a person goes, speeds etc.


For the TPMS, the method is use a SDR for packet inspection.
The tire sensor data is not secure and doesn't need to be. It's the car body-ECU that receives packets and at worst wrongly turns on the light for a few minutes, if the TPMS was spoofed. A LF 125kHz datagram wakes up the sensor for reprogramming, so it's near-field.

TPMS Receiver Hacking - Worcester Polytechnic Institute 2015 paper has some details (good references), and there's that Defcon 18 talk.

I found Python open-source to capture TPMS sensor data using SDR. https://github.com/jboone/tpms

Kinetis KW01 MCU designed for the TPMS application.

[labjr]

Autel makes several tools for TPMS  reading and programming. I wonder why there's not cheaper knock-offs of those tools? They get progressively more expensive as they drip-feed features which is probably just different firmware.

[aargee]

My car uses the ABS wheel speed sensors to determine if the tyre(s) are going down.
Probably not super accurate but I'm happy with that, all I want is a prod to go and check them.
Simple reset on the dash sets the new pressures.

But I agree, on board car systems are often like they're designed out of the 60s or by a workplace, health and safety aficionados.

[NiHaoMike]

My car uses the ABS wheel speed sensors to determine if the tyre(s) are going down.
Probably not super accurate but I'm happy with that, all I want is a prod to go and check them.
Simple reset on the dash sets the new pressures.

But I agree, on board car systems are often like they're designed out of the 60s or by a workplace, health and safety aficionados.

DIY indicators:
http://techno-fandom.org/~hobbit/cars/tpms/

[CJay]

Just wondering where you live in the UK that you need winter wheels?

[paulca]

Just wondering where you live in the UK that you need winter wheels?

It's less the climate and more the necessity that the car is usable in all weathers and ... it's a GT86.  It's designed to be a gripless wonder.  Light weight, rear wheel drive, under tyred, tail happy.

Also, it makes a difference.  Most people assume winter tyres are "snow tyres", but it's not about that.  Sure they have special centre threads for snow which lock snow into the tyre as the best thing that grips snow, is snow and why snowmen can be built.   It's about the tyre compound in low temperatures.  The summer tyres only quote performance down to 10*C below that the compound becomes rigid and hard giving a fall off in grip the lower they go.  The winters are only rated below 10*C and stay soft and flexible down below -10*C.  They are also much more progressive when they do let go, scraping across the road like they are grabbing every last ounce of grip with their finger nails.  The summers just instantly give up in the wet like, "You're on you own".  Also they have much better wet performance due to much better standing water clearance.

The biggest surprise I got was how well winter tyres handle ice.  Sheet black ice.  They have special little cleats or slits which grip the little airbubble noddles on ice.  Surprising amount of grip.  So much so that I had a false sense of security and fell on my arse when I got out of the car one morning.

[AndyC_772]

I used to work down a country lane which was never gritted, and which was in the shade of trees on either side. Every time it snowed, traffic would compact it into a layer of sheet ice which wouldn't melt for weeks. Add to that the fact that the road was barely wide enough for two cars to pass each other, and it had a few steep gradients too.

Winter tyres were a must-have, at least for those few weeks of the year.

[CJay]

Winter tyres were a must-have, at least for those few weeks of the year.

I think that's it, my partner lives in Shropshire and during the 'beast from the east' snow recently, it was treacherous, six foot high drifts at the sides of the roads, the main roads and motorways were compacted snow for a couple of days but it was literally only for a few days, we managed to get deal with it by just being cautious and driving (or not driving) to suit the conditions (slowly, very slowly) but if we'd been up the side of the Wrekin then it'd have been a different matter and a tractor might have been more useful

It was scary fun watching idiots in 4x4s and big German cars thinking they were impervious to the conditions and seeing their cars being towed out of hedges, barriers etc. the amount of 'street furniture' that got wrecked in that week was astonishing.

[paulca]

It was scary fun watching idiots in 4x4s and big German cars thinking they were impervious to the conditions and seeing their cars being towed out of hedges, barriers etc. the amount of 'street furniture' that got wrecked in that week was astonishing.

4 Wheel drive owners need to be taught that 4xfeck all grip is still feck all grip! 

I'd take a rear wheel drive on winters over a 4x4 on cheap summers in snow.

[Zucca]

I was a TPMS developer for 5 years (2006-2011): lots of discussions and meeting. I need to write a .pdf to comment everything here.
All the system I developed could manage 4x2=8 Tires in memory so no problem for winter/summer change. If you have a TPMS Reset funtion you HAVE to reset the system everytime you mess around the tires (refill or change).

Hacking a TPMS at radio level is not too complicated: there were 3 main providers for the market:  BERU, Schrader and Continental. Please do not do that, there are some collateral effect you don´t want, moreover there are much more easy ways to attack the beast as already commented.
All of them 3 main providers have propetary protocol and different working principles. At the end my TPMS adventure they were talking about a standard protocol compatible for everybody. After countless meeting and discussion I saw no agreement and I was pissed because lots of nice feature were going in the bin to make everything compatible back and forth.

The golden rule:

PV=nRT

this works almost perfectly in a air-tire (or the N2 bullshit low leakage gas) system. For runflat consider V almost constant, for non runflat there is a V change with P changing but not too dramatical (al long P remains in a certain range).

Anyway if T goes down P goes down and viceversa. If you ride after 15min the tires are warmed up generally (evet up to +20C from initial condition). So do not relfill your tire when hot, or if you do put something more to compensate.
Normally we are talking about 0,1Bar/10C. Please do your calculation regarding your local condition. Please remember the suggested BAR/PSI are for COLD Tires (not driven).

When the light is triggered depends on federal country law and system implementation. Normally there is a trigger when P-25% of reset value (if the car has a TPMS reset function) AND there is a low limit generally at 2,7BAR absolute (=generally +1Bar of ATM pressure, so 1,7 Bar when you read it with a normal manometer at the gas station).

Moreover what the manometer (tire gauge) says at the gas station is just the difference between the atmosferic pressure and the pressure inside the tire. The sensor has no clue what is the outside atmosferic pressure. We had issues when customers were filling the tires in Andorra (I was told cheap gas there and busy gas stations) at relative high altitude and then going down the mountains the tire were virtually loosing pressure...

Another golden tip: DIFFUSION. There are no perfect tires, the leakage rate is normally 1Bar/year but is depends if the tires are the giving traction or not (i.e. in rear traction cars the diffusion rate was 1,1 Bar/year and  in the front 1Bar/year). By knowing the T and P at the reset condition and the T and P in the tires it is easy to calculate how much pressure was lost due to diffusion or low leakage AND the P/T gradient.

The best TPMS system I know?
Check and look yourself your tires every month at least.