Subaru Repair: Subaru 2000 Outback- resetting check engine light, code scanner, test plug

Question
I need to take my car in for an annual emission testing.  They will not test with the check engine light on.  I know I have a catalytic converter issue as the car was my sister's and she had it diagnosed as such.  She would take to dealer and they would reset the light at which time she would promptly drive to the closest emissions testing station and pass the test. Is there a way I can reset the light at home?  There is a green plug under the dash which is unplugged, I replugged and and happened to be at the dealership and asked a mechanic what it was and he told me it is a pre-delivery test plug of some sort and should remain unplugged.  It caused the check engine light to flash and if I recall correctly caused the light to go out for a short time after disconnecting.  Does this make any sense to you?

Answer
Bob,


You have been misinformed and I am not surprised as most don't understand how the computer works.

When you turn off the light you also turn the emissions monitors to not ready status.  

If you try to take the test with the enough of the monitors to not-ready status it will fail the test.

You don't have to take my word for it, but a cheap code scanner at a parts house, clear the light and drive right over to the test station and see how it does.

Why not repair the car? I realize it's only clean air.

If the code is cleared and the memory dumped the vehicle must be driven until the monitors are turned back on.

The green plug is the D-check connector it puts it in D-check mode.