PLEASE NOTE: This post is for interfaces that respond properly to all ELM commands in my "Test" which is in the Settings dialog (all commands should have response OK). Please, someone with knowledge in the circuits to explain these better as I don't have time for more details. It was also reported by many users that the problem can be solved by simply removing the 120 Ohm termination resistor (which is connected between the two CAN lines, it is R14 on my photos but might be marked with different number on other interfaces) from the interface. NOTE: It is reported that most of the new interfaces now have this problem! I did it in a hurry just for the so don't blame for the soldering quality on the pictures. I did it directly on the OBD connector as it was easier for me. Remove the single terminating 120 Ohm (or whatever) resistor from the interfaceģ. Get two resistors of 100 Ohm and 2 capacitors of 560 pF. So i just got two 100 Ohm resistors and two capacitors of 560 pF and fixed my interface as shows below. The problem is actually in the CAN termination method used in these interfaces - they use one 120 Ohm resistor connected between CAN-L and CAN-H.Īccording to the ELM327 datasheet the proper termination is to use 100 Ohm resistor on each of the 2 lines connected to ground through a 560 pF capacitor (see the picture below). 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.
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