Modern Tire-pressure monitoring system Sensors: Let's try a DoS attack | Hacker News Reader

Modern Tire-pressure monitoring system Sensors: Let's try a DoS attack

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61 pointspabs334 comments

I bought a USB SDR-dongle a couple of years ago, primarily to monitor aircraft, and similar things.

Running a simple sniffer, trying to identify all the things transmitting locally was pretty fascinating. Prior to buying this I had no idea that tyres transmitted data via radio-waves (is it obvious I don't drive?)

I setup some wireless temperature sensors which transmit over 433Mhz, but eventually abandoned them. It was just as good to sniff the temperature-reports the tyres in the carpark beneath my flat were transmitting!

Wait the TPMs also send temperature reports? That's pretty cool. I wonder how many you could see with a decent receiver, if they interfere with each other at range, if you could get a solid temperature from a few dozen low-quality sensors etc.

>Wait the TPMs also send temperature reports?

Tire pressure measurement doesn't make sense without temperature.

Yep. pV=nRT. This is why if you are checking your tire pressure manually you should do it when the tire is cold, and not immediately after a drive. "Cold pressure" is how the vehicle manufacturer's recommended tire pressure is specified. You'll still get some seasonal variation in most temperate regions.

I get what you mean, and I haven't had a car in a while, but the last one I had, the TPM didn't seem to correct for temperature at all, and would flag all the tires as being low on first start on cold days.

I would have thought it would be better and easier to do environment temp monitoring and some heuristics in the central controller rather than put a temp sensor on every TPM and add temp data to the transmission protocol. Ex expect lower pressures when the exterior temp is cold and the engine is cold, expect higher when the engine is hot, etc.

What makes you think the pressure wasn’t low at start? After driving some distance your tyres will warm up and the pressure will increase.

That's the point. It was low, but that should have been expected due to the low environmental temperature. The warning system should know that it will increase to the proper levels when the tires warm up some and should not request that I inflate them further.

I guess that depends on what the software that reads the sensors should say. If you like automatic transmission, perhaps you’d like the sensory to report inflate/just fine. While if you prefer to shift gears yourself you might prefer a more direct reading so you can decide for yourself.

So conversely would you want to be warned that your tires are too low when its warm because if it were cold they would be under pressure?

Would you recommend a sniffer?

Would I recommend it as being fun/useful? Yes.

Would I recommend a specific model? I'm not too familiar to be honest. I want to aliexpress and picked the cheapest USB RTL-SDR dongle I could find. Paid €5 or so for it, with a tiny little antennae.

I’ve used the very cheap RTL-SDR dongles sold as TV receivers.

Ones I use (that work well) look like this: https://m.aliexpress.com/item/1005001815260665.html

For those on laptops that were confused by the humongous images, buttons and font on this link, try this non-mobile link: https://aliexpress.com/item/1005001815260665.html

the rtl-sdr.com v3 dongle is a good specific hardware model to seek for general purpose "i dont know what i want to do with this" use. there's others with other strengths when you get more specific.

Difference in pressure between tires is affecting safety and lower pressure in general affects fuel (noticeable even on single car; overinflated tires can give up to 10% economy in long range rides) and tire maintenance cost.

I wonder if tire pressure sensors get special treatment in modern EV both from the range perspective and from the fact that tires are the only thing you have to change regularly in EV.

They don't get special treatment. I think the new Volkswagen ID3 does not even have tire pressure sensors, they use other systems to detect a leak.

TMPS is mandatory on european cara since 2014

TPMS is mandatory unfortunatly no sensor is needed for that. Here is a good german article about that: https://www.adac.de/rund-ums-fahrzeug/ausstattung-technik-zu...

basically the following vendors only use indirect control systems (no sensor): VW-Group (VW, Audi, Seat, Skoda), PSA (Citroën, Peugeot, DS, Opel), Fiat, Mazda or Honda. the problem with sensors is that a new set of tires have additional cost of 120-300€ which is most often not an issue since the vendors who use direct control systems are mostly premium vendor cars.

Yes. But you can monitor the pressure indirectly without a pressure sensor, by comparing the rotation speed of the wheels. Wikipedia says that a flat wheel has a smaller diameter and rotates faster. https://en.m.wikipedia.org/wiki/Tire-pressure_monitoring_sys...

It's cheap and not great but it's a valid TPMS system for Europe.

The US spec requires detection of deflation independently, so indirect isn’t allowed as underinflating all 4 tires can’t be detected by indirect means.

Honda cars sold in the US use an indirect system that works exactly as he described, so it must be allowed or Honda has gotten away for years flagrantly violating the law.

NB: if you have one of these systems be on the lookout when you get your tires changed; a lot of chains will try to charge you for the tpms sensor when you don’t even have one.

Some indirect systems use the first 10km driven after changing tires as a reference. Those systems can detect all four tires deflating at the same time, however, they need to be explicitly told via a special key combo or a diagnostic interface that you changed the tires just now. Maybe that is what they are trying to charge for.

Nope - they've never even seem to have been aware of that system, never activate it, and they charge per tire.

At any rate, at least on the cars I've owned, it's been something along the lines "hold down this button on your dash for 30 seconds", so I'd be pretty irate about being charged for that even if they did it.

Indirect TPMS does not need radio transmitters like this on the wheels.

Under-inflated tire can be detected using the ABS sensors and software.

https://en.wikipedia.org/wiki/Tire-pressure_monitoring_syste...

Afaik, TPMS does not follow a specific standard for communication. I saw a video about tpms and privacy issues. Because each sensor have a unique id, and beacons it out every minute. With four weels, you have an unique is every 15 seconds or so. The industry response was that it was an unreasonable attack since each car brand had their own protocol. Well, the rtlsdr projects now can decode a dusin. But my point was, that since there is no standard on how tpms should communicate, why would there be a regulation dictating it do be done in a specific manner? The end goal is that the cars drive with correct tire pressure.

ABS speed sensors are sensitive enough to determine tire pressure

I worked at a company that was developing TPMS and also made traction control and ABS systems in another building. The TPMS group was part of the lobby trying to get these required on cars while the guys in braking told me they already detected low tire pressure passively without a sensor. Not every vehicle had those ABS systems, but TPMS still seemed like a product looking for a market.

Putting a distinct serial number in each one, that could be read at a distance, was a clever idea to appeal to a certain segment of government.

Mazda uses the ABS data instead. Which I prefer, because otherwise you'll need eight sensors already, if you switch between summer and winter tires.

My 2014 Jetta used the ABS system like this, and it blew my mind after having dealt with failed Nissan TPMS sensors all the time.

Usually you have a crummy-but-good-enough encoder on the wheel in the form of a steel tone ring and a magnetic pickup. If you know the steering wheel angle and can observe the relative rotation rates between wheels, you can infer which tire is low. How do you determine that all of them are low? I guess you could compare against a GPS velocity?

I guess when all of them are low, you are either neglecting maintenance of the machine you got a license to operate or you won't drive anymore...

Designed a transmitter to spoof TPMS, in this case, for my own car : https://github.com/gcormier/tpms_silencer

This way when running my winter wheels/tires, I don't have that annoying light. Alternative : black electrical tape, but where's the fun in that?

I have a car with these sensors; they don't work, probably batteries are dying (car is 14 years old). Just another nanny lamp on the dash that I ignore.

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