Mont is right, in factory efi vehicles the modules all have a seperate ground going to the battery. They are joined to gether with a splice comb. the body/frame is grounded and the starter and engine and fan motors, etc.. use frame/body grounds. On computer data lines they are ALL twisted pair and on the newer CAN bus sytems the ecm and bcm(some times the ebcm) will have a 120 ohm resistor in both modules, these resistors make the the data lines have even less noise. Also a sensor ground is not a standard ground, it will have an inline transistor to remove noise and it is a "higher ground threshhold" than a normal ground. Then when you get into 5v referenced systems and double redundant 5v reference systems your head starts to spin LOL!