i got a 98 legacy 2.5 gt and the cat as bin remove some time befor it was mine so there for i wan to find what resistance or with diode that would mimic the signal that the post cat sensor would send in ideal condition to the computer

post cat 02 sensor

It's not a resistance type of device - it's signal is a sine wave that bounces between lean and rich. You can't approximate it without a signal generator circuit.

 

You could put a non-fouler in the exhaust before the sensor to pull it out of the exhaust stream and that will fool the computer if your exhaust is clean enough.

 

GD

Yeah do the spark plug non-fouler trick. Lots of info about it here if you search for it. People use the non-fouler to get rid of the P0420 code. If you search for P0420 you should get some info about it. But basically it's a 14mm (I think) non-fouler threaded onto the end of the rear O2 sensor.

 

If the car doesn't have a rear O2 sensor (because it was removed) you'll have to get a signal simulator to get rid of the code. You can buy them at tons of places online, but they are usually kinda $$$.