I got myself on of those cheap Bluetooth OBDII dongles but it didn’t work in my car (2005 Dodge), it simply couldn’t detect the protocol which is SAE J1850 VPW used on most Chrysler/Dodge I believe before 2008. So I took it apart and as you can see in the picture it has two stacked circuit boards the one of top has a bluetooth chip (BEKEN BK3231Q) and a CAN protocol transceiver from NXP (TJA1040)
The flip side of the top board contains a CAN controller (MCP2515) from Microchip.
However, and what is surprising is the bottom board which contains only voltage regulators for 5v and 3.3v and most of the OBD-II pins are not even connected!
Let’s compare the connected pins to the pinout of the OBD-II connector in the image below
So the 12v VCC (pin 16 in red) is connected and the two ground pins (pin 4 & 5 in gray). How about the different OBD2 protocols? let’s see:
- CAN (ISO15765) used pin 6 & 14 (green color) and they are connected.
- ISO9141/14230 uses pin 7 & 15 (yellow color) and they are connected.
- J1850 PWM uses pin 2 & 10 (blue color) and they are NOT connected.
- J1850 VPW uses only pin 2 (blue color) and it is NOT connected.
So it is clear that this will not support any of the J1850 protocols which are used by most old American car makers (Chrysler/Dodge/Jeep, Ford, GM), luckily I think all new cars (2008+) are using the CAN protocol which is the newest among the others.
Update: Another fake OBD2 reader
I bought another Bluetooth OBD-2 reader that is slightly larger than the one I got before hoping it would have the parts needed to support all protocols and since the seller also claim it does. (Spoiler: I got a full refund).
Guess what? It is exactly the same as the other one, it didn’t work on both of my cars so I opened it up and unsurprisingly it has the same guts (same chips) in slightly different arrangement. 
I think having full support is a little too costly even for the Chinese manufacturer, also don’t be fooled by some sellers on Amazon who sell the same exact models for $15+, increasing the price won’t make it work. I also won’t recommend using these basic devices in your car since they don’t have Bluetooth authentication! and any nearby hacker can connect to them and have full access to your car CAN bus and do whatever your car manufacturer has allowed on that bus. You might have heard about the recent car hacks like disabling the breaks and such.
So if you are looking for something that works with all protocols and also safe to use I would go with trusted brands that have been tested by many users, e.g. “OBDLink LX Bluetooth“ which looks like the perfect solution, good quality build, support for all ODB2 protocols, sleep mode and has a security button that need to be pressed to allow Bluetooth pairing I have not used it though since it is a little expensive.