Okay so checked the voltage at the pins on the OBD plug they all get power ~12V except for pins 4&5 (2 black wires). If you're looking at the plug that would be the top 2 middle pins on the short row. Voltage at the fuse is good and the fuse ohms out good. Im gonna chase the 2 black wires as best I can. I kinda have a hunch theyre the ones that a scanner talks to the car through but who knows.

 

Black is ground, 4 and 5 are just that. In the past comm problems were caused by corrosion on the board, usually so severe though the engine wouldn't fire, case/covers rotted away. If it where mine I'd pop the covers and have a look, never know.

 

Yea i popped both covers open last week and it looked brand new inside. The ECU has a sticker on it that shows some vin digits but they dont match the vin on the rover. Which is weird because the only two people who have owned it are my dad and myself and he doesnt remember anything about the ECU being replaced. Wondering if the dealer did something fishy along time ago. I also checked to see if both of those grounds matched the vehicle ground and they didnt so something might be going on there.

 

E200 and E201 are the ground locations, RH and LH footwells behind the kick panels.