When you perform the identical test using the hardware serial port, is the command string, i.e. "atrv" echoed back from the serial device? If so, my theory is that the "noise" you are seeing is this command string being corrupted.
Yes! That's a detail I forgot to mention. In this case, I get this:
But I didn't understand how can the OBD cable get fine what I send through NewSoftSerial, .e.g. the ATRV
command, return the expected value and JUST corrupt the echoed command.
I would like to understand. I'm not the kind of person who just leave things half-made. And I really want to make this NewSoftSerial works right, even if it's working with Mega2560.
And Paul is correct; you should not touch any pins whose control you have turned over to NewSoftSerial (or any other library, I would think).
Yes, I agree, but was just an attempt. This is why I commented out after seeing it doesn't work. I will remove it anyway, to avoid confusion.
Thank you again.