98 850 gtl scan tool cannot read pid
 

I bought a 96 850 gtl , when I took it in to have it smogged the smgg tech pulled me over to show me some issues . I have never seen a car do this said the tech... All the gauges when crazy when the odb scanner was plugged in, the speedometer went up to 70 mph, the heat gauge when to hot, the fuel gauge dropped to zero and he couldnt see any of the "live Data" or the freeze frame pid, Now I had a couple codes pop up and fixed those issues,, and could clear the codes. My car is running great, no codes etc... but now I cannot read the pid on any scanner. Is it a ground issue or a ECM issue. I only have until 2/20/19 to fix this that is when my extension runs out. I cannot return the car as I bought it at an auction a friend took me too, any thoughts on this