Well, it seems that the problem is electrical and is not very hard to fix.
I also have one of these 'faulty' units and decided to play with it and see what is wrong. There was one user here who bought 5 of these cheap interfaces with no luck and finally bought an expensive one. A lot of people are having problems with some chinese ELM interfaces that cannot connect to CAN network even if they support all ELM 1.3 commands properly.
