If you want to use GOFAR and another OBD device at the same time then you would need a splitter to plug two devices into the same OBD port.
This is however something we don't recommend doing. You could be sending two data streams to your car and so the splitter would need to act as a data traffic cop and very carefully organise how the data goes to your car to avoid the two streams causing potential confusion.
We cannot test GOFAR on all the possible device + car + splitter combinations so at this point we do not support using GOFAR with a splitter device. GOFAR's awesome on it's own but if you feel there's a feature missing that you'd love just email firstname.lastname@example.org!