Selecting OBD adapter
What is "ELM 327"
ELM327 is an OBD to serial data processor designed by ELM electronics. With it, ELM electronics also defined a set of instructions/commands to be used as the interface to access the chip.
OBD adapters that equipped with ELM 327 chip are often considered 'real', 'original', 'proper', while others are considered 'knock off', 'clone'. Extra caution should be exercised while dealing with vendors who claim to use the real ELM327 chip in their adapters. We came across a few of those in the past and they all turned out to be lies. At the moment, pretty much every ELM327 adapter you can buy from the internet does NOT contain the actual ELM327 processor.
ELM 327 compatible adapters from ebay/amazon/banggood/gearbest/DX/Aliexpress
Buying an OBD adapter from these websites can be quite confusing. They often came in different packaging formats, some larger, some smaller, some with 5 LEDs, some just one or no LEDs at all.
v2.1 compatible adapters .
We have a few v2.1 adapters, none of the v2.1 compatible adapters we tested provide full compatibility to ELM327 instruction set v2.1. These adapters only support a very small subset of ELM 327 v1.0 instruction.
These v2.1 compatible adapters are quite similar even thought they came in different types of plastic packaging. They use a Beken 3231 Bluetooth chip in conjunction with MCP2515 CAN controller. There is no dedicated PIC for ELM emulation. The firmware that emulates ELM327 instruction is stored and executed by the small MCU inside the Beken Bluetooth chip.
Despite vendor claims of supporting all protocols, two of these v2.1 adapters only have the CAN wire connected, which make them unworkable on older vehicle that uses J1850 or ISO9141 protocol. We also found that these adapters have lot of compatibility issues when trying to connect to older vehicles using custom init strings.
Another issue we should note is that these v2.1 adapters all seem to have a very small memory buffer to process OBD messages, make them easily crash while reading some diagnostic messages from CAN vehicles.
v1.3/v1.4/v1.5 compatible adapters
These are often considered 'older' adapters. we found them to be somewhat better than the newer v2.1 adaptors. The ones that we tested support more ELM instructions, and have faster connections. These dongles all have a dedicated PIC to emulate ELM instructions, and in that they provided better compatibility.
If you are considering buying OBD adapters for vehicle does not use CAN protocols (vehicles manufactured before 2008), check out adapters from OBDlink or BAFX. These adapters are more expensive but seem to work much better in terms of vehicle compatibility and connection speed.
Wi-Fi or Bluetooth?
OBD dash support both Wi-Fi and Bluetooth adapters, each type has its own advantage.
Wi-Fi adaptor is easier to setup specially on Windows 8.1 and Windows RT. Setting up Bluetooth adapter on Windows 8.1 can be very frustrating and often result to connection failure with no warning (see how to pair Bluetooth adapter page for more details). On the other hand, Wi-Fi adapter is more expensive, and some what slower than the Bluetooth adapters.
Bluetooth adapter usually faster than the Wi-Fi adapter if set up correctly. It also allow you to use network for other activities while using OBD dash.
