This $11 car gadget can save you money

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These are great and I have a handful. Should be noted that leaving plugged in is a bad idea. They start up in pairing mode and will connect to any nearby device meaning someone near you at a stoplight. This wouldn’t be a big deal usually except some newer cars have a CAN bus which this device can inject commands into to unlock doors, operate windows, shut engine off, turn radio on full blast. Also, some cars power your ODB adaptor while off (Roadtrek camper) and makes it rather easy to get in a locked car.


It’s such a frustrating boy-who-cried-wolf. Back in the Filmore administration when I took high school drivers Ed that check engine light was like the doomsday warning. Now it lights up for every damn thing. I swear it comes on for bad breath or a parade nearby. Black electrical tape is such a tempting solution.


If you really need an OBD reader, spend the money for a good one, and work on your car. If you just want basic info and to clear a code, just about every auto parts store will let you use theirs for free if you give them your driver’s license as security.

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Here is some more info (from something called boing boing?) about why you should not leave this plugged in when you leave the car:


Oh, wow! I thought these cost a couple hundred bucks…

Do the cheapies actually allow you to have a suitably unmediated chat with the CAN bus?

My understanding was that you’d typically get an ELM327 or STN1110(or, on the low end, any one of a number of more and less quirky clones, probably of a relatively early revision of the ELM327) connected either to a BT radio acting as a serial link, or a USB/serial adapter; with access to at least a reasonable percentage of the OBD-II codes that are mandatory and standardized probably working; but things getting less likely as you push further into either vendor-specific extensions or the ability to chat with CAN peripherals not at the OBD address, much less craft raw CAN output.

There’s no way in hell I’d want an untrusted party to have CAN access; but I’d been led to believe that most of the basic ODB diagnostic dongles, especially in the cheap seats, sacrificed the versatility of a full CAN adapter(typically only available in suitably equipped microcontrollers and SoCs, or surprisingly expensive as a PC add-on) in favor of cheaper, less timing sensitive; but less versatile options(and then cut some corners, as only the finest chinese cloneshops know how).

Have people been slandering these devices to me? Do they mostly deserve that reputation; but enough clever hackery and exploitation of corner cases that successfully pops the trunk on common vehicle models has been demonstrated that security-through-inadequacy is still not assured? Is the attack not presently publicly known; but plausible enough to worry about, and even if it isn’t possible you still don’t want to drain your battery?


I’m not an expert(someone please do correct me if I’m wrong); but my understanding is that the advent of phone-based software has made a very, very, substantial difference.

A standalone OBD-II diagnostics device can, indeed, cost anywhere from ‘a fair amount’ to ‘You wouldn’t even want to know; and since you aren’t an authorized dealer, we won’t tell you’; but most of the price is the software and the knowledge of what the OBD codes actually mean(some are public knowledge, some are manufacturer proprietary with varying degrees of reverse engineering by outsiders, who are more willing to at least sell; but not necessarily inexpensively). Once you wrap all the software and data costs up, provide some flavor of embedded system for the stuff to run on, and a little screen, you are indeed looking at a fairly costly device. As far as I know, devices like that still are pretty expensive; and the official, manufacturer-blessed, dealers-only, system is likely to be Very expensive.

The hardware needed to merely talk to the CAN bus reasonably safely is fairly minimal(the original ELM part was implemented on a PIC microcontroller of no particular heroism, this isn’t a high speed bus); and the additional bridge hardware(something like a MAX232 for serial, probably an FTDI clone for USB, or any one of a number of bluetooth slave ICs for bluetooth) only adds a few dollars more. Such a device does nothing useful by itself; but when combined with the phone you already have, running software that is now priced more in the ‘app’ range and less in the ‘industry-specific shrinkwrap software’ range, it provides much of the same power as at least the lower end standalone devices; but for peanuts.


The last I had heard about prices, it was something that would have connected to my Palm III. That was a fair bit of time ago.

$11 and it connects to my phone? Yikes.

What do you mean “would have connected to my Palm III”?! PalmOS 4 lyfe!

Bastards can have my Visor Edge when they pry it out of my cold(fire) dead hands…

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Eh, you kids and your newfangled contraptions! I had a Palm IIIe (special edition), and it could run LIFE, LISP, take notes, and sync its calendar with my PC.


Oooh, special edition. Much respect.

And subhunt. You said what it could do. I know what it did do…


Yeah, I am not sure why it is called a “Check engine” light anymore. It used to mean you car was about to burst into flames and die. Now its more of a “maintenance needed” light that is so bright you can’t drive at night without being blinded by it. Mine has gone on almost exclusively for O2 sensors working poorly.


Nice phone.

What will a good one do that this one will not?

Really, I’m just happy when I see an Android only device.


It looks like the one Mark linked to is just a rebranded version of this one (a few dollars cheaper, but ships from China). It is indeed an ELM327. Also, the one on Amazon is now $13, not $11.


Here are some other Amazon options:

OBD code readers are not a panacea. You could get an error code that means X but the problem is actually Y, that makes X misbehave. Still some searching on the internet and if you are mechanically inclined it can save you some repair bills.

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A lot of those ship from China as well - you have to look closely at the seller.

Edit: not that shipping from China is bad, it just takes a long time if you’re in North America.


I cannot, in good faith, consider buying any product that comes with the warning: “Throw away a part of the product, it may or may not have been designed to attack your entire life.”