This post starts with this question reading:
I have a 2001 740iL and i have both BMW 20pin and 16 pin in the engine bay and interior of the car. i have a scanner with the 16 pin obd2 only. Can you help me with the difference in these 2 connections? Should I use the 20 pin instead of 16?
Followed the professional answer on how to choose BMW round 20 pin or 16 pin obd2
Depends what your scanner is capable of.
The OBD port can communicate to Engine Control Module and automatic Transmission Control Module only.
The BMW 20-pin port can communicate with engine, transmission, AND all other modules (airbag, traction/ABS, etc).
Keep in mind that most generic scanners only read emissions related codes that only require OBD. A BMW specific scanner will read more modules through your 20-pin.
BMW scanner I own:
I have a k+d can cable that I will plus in my laptop with ISTA d or ISTA p. I was advised that If my car has a 20-pin port present, I need to use that (K+DCAN cable with 20-pin adapter is fine) to access all modules; especially with ISTA, since ISTA scans all modules.
I also need to check if pin 15 in the round plug is populated. If it is I will need an ADS interface for certain modules. The most common one I have found to still be on ADS in the late cars is the ASC/DSC.