OBD scan tool not communicate with modules? Diagonose the K-Line communication Bus.
see the K-line bus waveform on the oscilloscope and voltage fluctuation on the digital multimeter.
if your OBD scanner not communicating with the modules? it might be bad K-line bus. specially early EFI Cars as well as some modern cars also use K-line communication bus for talk to the OBD scan tool.
try to trace the K-Line bus in this way we discuss in the video.