OBD readers - Topic split from Community News, 30th November

An OBD II device based on ELM327 hardware in its last version 2.3, it is hard to find but v2.1 came with €4 and has the BT to communicate with the app. Unfortunately, almost all of them just display values but do not allow any interaction in their free version. However, kernel 6.x in the last version had integrated the driver, I suppose this one:

Here the news

I have bought this one because the previous was too old: v1.5

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These devices are fake. They are not really ELM327 compatible and do not support proprietary protocols. You need proper ELM327 compatibles such as Konnwei KW902/903.

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That devices are Chinese clones, so what’s wrong about that?


Possibly, but most of them have the same board design and they are a good starting point.

It cost x10 times more than a Chinese clone. It is a huge difference for a learning toy.

Supposing, you are not serious in “use a professional plug!” for “hacking just for fun” your €60K car on which you drive around yourself and possibly your family as well.

It costs 10x (€15) but at least it works.

I bought several Chinese clones (including the one you show) and had to throw them in the bin because they did not work, which means that the €1,5 I paid for them were €1,5 wasted.

By the way, I used my Konnwei KW903 to add an additional FOB key bought on AliExpress to my car. The original key would have cost €350 plus €50 for programming.


That package is common to many clones, not just one.

What does it mean for you, exactly? Oh, I see.

Which is the reason for which “Konnwei KW903” is not a suggested learning tool.

It can change the settings of your car, for real. However, we can take a look to Amazon:

4.6 €120
4.5 €46
4.0 €37 (KONNWEI KW903)
3.8 €10 (Mini ELM327)

Trusting the users, the gap between 4.0 and 3.8 is not as significative as 4.0 to 4.5/4.6

Moreover, those need to make changes, are better they go with something like this:

Which cost as much as a good dongle which requires software and skills but still errors prone.

While an embedded instrument, might solve or not but it is supposed to work and makes no damages.

We are going off-topic, however that tool is not vendor-specific but only generic OBDII, therefore works like cheap pseudo-ELM327 tools which do not support vendor-specific protocols. It will read and erase error codes and vehicle metrics, but will not allow vendor-specific tweaks. For vendor-specific protocols, mobile phone or PC software (vendor-specific, AlfaOBD in my case and for ex-FCA Stellantis cars, others for other brands) is the best choice.
KW903 is currently available at €13 (including shipping) on Aliexpress.
Comparable dedicated tools are the like of this:

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Interesting. Lack of standards, as usual. What do you think about this one:

It seems supporting a lot of standards. Might that “tweaks” part of that standards, instead?

Those are for the physical interface. Proprietary protocols sit upon it, just like OBDII, so you cannot tell until you test. The real ELM327, KW903 and other “full” interfaces support proprietary protocols (through CAN USER1 and CAN USER2), cheaper clones only support OBDII.

About protocol based on CAN bus, here a list:

Note that the ELM327 can handle communication
over multiple protocols, not just CAN:

    Protocol - Description
    0 - Automatic
    1 - SAE J1850 PWM (41.6 kbaud)
    2 - SAE J1850 PWM (10.4 kbaud)
    4 - ISO 9141-2 (5 baud init)
    5 - ISO 14230-4 KWP (5 baud init)
    6 - ISO 14230-4 KWP (fast init)
    7 - ISO 15765-4 CAN (11 bit ID, 500 kbaud)
    8 - ISO 15765-4 CAN (29 bit ID, 500 kbaud)
    9 - ISO 15765-4 CAN (11 bit ID, 250 kbaud)
    A - ISO 15765-4 CAN (29 bit ID, 250 kbaud)
    B - User1 CAN (11* bit ID, 125* kbaud)
    C - User2 CAN (11* bit ID, 50* kbaud)

Comparing this list with the one shown in the dongle image, just the last two are missing.

About the KW903 is available in many different sub-codes:

J6D3 B2I7 T5X5 Q9E4 E3C6 J6D3 
B2I7 T5X5 T7U6 F1Q1 F8V9 K6V5 
B8T7 D0G4 J5Y6 R2I0 G0K0

Does this codes make a sense for you?

From the same Arduino forum, also this seems interesting:

ELM 327 and STN21X are good option for read the CAN data.

And the STN21X brings here:

and the most appealing product ($90) is a combination of dongle + software for “OBDLink LX Bluetooth Scan Tool” which a way better approach of buying a dongle and an app separately.

Moreover, they present a list of cars and car makers supported:


A physical interface would this one:

The USER1 and USER2 CAN are just protocol on the same physical interface.

In this sense the dongle act like a modem with AT commands. If its set of AT command supports the activation of USER1 and USER2 CAN protocols, then it can communicate also with that two protocols. However, this does not means that the software connected to the dongle can interpretate the received messages.

Some interesting links


One of the most comprehensive ODB scanner that supports many protocols included the RAW CAN (ISO 11898) which is a great for those that wish to make their hands dirty at the lowest level is this one:

Me to. I also bought a Chinese clone that didn’t work.

On AliExpress happens frequently. Try TEMU, they have a better quality check about vendors, IMHO.

No thanks. I bought a “no bluetooth” dongle that actually works.

Heh. My vehicle (the one that is not a bicycle, skateboard, skis, or shoes) is so old, it cannot be connected to any of those things. Thank god. I have enough issues chosing oil (ah, always 5w30?), hydraulic fluid (eh, the green stuff?), ah, you get the idea. Sigh, the T4 is in the garage cause I haven’t got an arc welder and the correct size pipes.

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I did not read in details, just over what was written and indeed, I had a car electronics course in 2011. It seems nothing changed since then. When buying the OBDII reader I read many warnings about the fake chinese clones. Also that vendors manage to secure their chips, so that the chinese do not work.
I also bought one with cable (USB2) which was more expensive, but works. In general you want a reliable dealer. It doesn’t matter if it is on AliExpress, Amazon or whatever.
Also as stated in the posts above, the OBDII provides standard information but does not give you all access. AFAIR it talks to the gateway. To be able to access different controllers in the car, you need a special software. It would use the same OBDII interface, but there is vendor specific part to go beyond the gateway. So to just read common error codes, delete them etc. or access generally available data like speed, temperature etc. you are good to go with a good quality ELM327 device (lets say genuine)
AFAIR they cost about 50 or may be 100,-
If you want to be able to do more … get something professional. It is even worse than that. Car manufacturers sell their own devices - this is why you have authorized dealers and repair shops. And this is why they charge that much. The probability to damage the vehicle is not to be underestimated.
For the rest the genuine ELM327 is sufficient. I mean if you do not want to reprogram a key or controller. Actually find a tuner in your area - he would have the right thing and information. For couple of bucks you’ll save time and trouble, if you know what you are doing.


Guys, anyone have problem with connection ELM327 adapter via Bluetooth to armv7 device?

Can’t create RFCOMM TTY on
rfcomm --auth connect (mac address) 1
As i tested, on all was good and it worked, with same OBD adapter.

No, sorry, i did want to reprogram a key.

Well I still stay on for many other reasons. I’ll add this one to the list, although I do not use BT OBD reader. Also it is not very comfortable to have a cable plugged, but believe me, it is the only way it works 100%

don’t know what car you have, but this is not trivial work. You need a professional equipment for that.
Each brand model has it’s own procedure and some even own hardware - for obvious reasons.
Not that it is impossible, but still it is very delicate task.
If the car shop is too expensive, I would look for a tuner. The software they use could possibly do that.

Have qt5-qtconnectivity-qtbluetooth reinstalled?

Sure, yes, without it OBDFish is not starting. But before OBDFish i need to connect ELM327 first via bluetooth. But it fails. Connect and after 2 seconds fails. Udev rule added.Rfcomm.conf added.
Terminal says:
Can’t create RFCOMM TTY
on default user, on root, with rfcomm --auth --raw option or without it too.