Beware of fake ELM327 OBD-II Bluetooth adapters

Cheap ELM327 compatible OBD-II Bluetooth adapters that connect to your car for diagnostics and retrieve engine and other data are available all over the Internet. But today, we were reminded that many are fake with a partial implementation or not working at all.

ELM32 was originally created by Elm Electronics – which recently decided to close shop – and based on Microchip PIC18F2480 microcontroller to provide the data through a UART interface, but copies have been around for years, and I myself bought a cheap ELM327 compatible ODB-II Bluetooth adapter back in 2013, but I never managed to make it work.

Those were brought back to my attention today, as Jasbir bought two such fake ELM327 adapters on Aliexpress for under $3 each. The device reports itself as ELM V2.1 with firmware version “TDA99 V0.34.0628C”, it’s extremely buggy and certainly not feature-complete for an ELM V2.1 device.

When he opened the device it was mostly empty with just a tiny board.

Fake ELM32 OBD II Bluetooth Adapter

But he was expecting a board with a microcontroller (the round chip covered with epoxy), a Bluetooth chip, a CAN transceiver, and other chips as shown in the photo below.

Working ELM32 OBD II adapter
That’s what the board inside a working ELM32 adapter should look like

Let’s have a closer look at the tiny board in the fake ELM327 adapter.

Single chip 16 pin ELM327 board

There’s apparently a single 16-pin SOP chip connected to a 24MHz crystal that handles everything…, and that probably means a software CAN bus implementation prone to errors and limited data rates.

Since the microcontroller is unmarked, Jasbir spent some time trying to find out what it is exactly, and it appears to be the same “QBD255” MCU as found in the Thinmi C OBD2 ELM327 adapter whose PCB is appropriately named “ELM327-Cheap”. QBD255-based ELM327 adapters do show on a web search on Amazon and other shops, but when clicking on the link, they’ve all been taken down.

However, it’s unclear whether QBD255 is an actual MCU part, as there’s a dearth of information about it. There is another SOP-16 Bluetooth microcontroller that looks similar: Chenbing AC6939B used by ElectroBoy on with information in English, but I can’t find any reference to AC6939B in ELM327 devices.

It’s close to impossible to spot fake ELM32 OBD-II Bluetooth adapters from the description or photos from an online shop (unless the internal photos are shown and/or the chip is listed), but if a device just costs a couple of dollars it might not work as expected, and if unsure, it’s best to purchase from a shop where you can return the items easily.

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9 Replies to “Beware of fake ELM327 OBD-II Bluetooth adapters”

  1. Simply buy ELM327 V1.5 adaper version if you want it for an old car. It’s based on a cloned original ELM firmware modified to run on a cheaper microcontroller.

    2.1 versions on ali are a 100% chinese product with chips from the bottom of the trash can and some broken in-house developed firmware.

  2. Just buy the cheap fake ODB-II dongle for the case and connector and replace the bad PCB with something like this:

    * ESP32 CAN board fits into OBD-II dongle, supports auto shutdown

    * WiCAN ESP32-C3 CAN Bus platform is available in USB-CAN and OBD-II form factors (Crowdfunding)

  3. Since I have a few of these, I’ve found the “ELM327 Identifier” app on the Google Play Store helpful for determining these devices capabilities / limitations. Some are simply broken e-waste though as you rightly point out.

  4. I recently bought this adapter for an extremely low price(model V01L4), its main MCU is an JieLi AC6969C2 (AB21BP0G286-69C2 on the IC, no datasheet available) and is paired with an SIT1044 CAN comms chip. It appears to work and ELM327 Identifier says it supports up to v2.2. It is also a dual mode BT device, with BR/EDR/LE.

    I also did some digging around on chinese alibaba and found that there are 3 primary variants that are based on the SIT1044 chip.

    One is the model mentioned above, it supports claims to support SAE J1850, ISO 9141, ISO 14230-4, ISO 15765-4 and uses Bluetooth. Model V01L4 (Translucent blue), V01B4 (White), V01L4 (Translucent black) and V05L4 (Translucent blue, mini)

    The 2nd variant is a Wi-Fi based model with a WinnerMicro W500 MCU instead of the AC6969C2. Model V01HW5 (Translucent black) and V05LW5 (Translucent blue, mini)

    And the 3rd variant is identical to the 1st variant except it doesn’t support SAE J1850. Model B02L4 (Translucent blue)

    Just thought of sharing this info here, as it seems like not all cheap ELM327 clones are duds.

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