Subaru Test Mode with Green Connection
Two green connectors under the passenger side will put your Subaru into diagnostic mode.
The two connector puts your Subaru into test mode to diagnose components that the ECU controls such as the secondary air injection pump and fuel pumps.
Green connection status:
Plugged in = Test Mode Enabled
Unplugged = Not Test Mode Disabled
How to go into Test Mode?
Connect the two green connectors under the passenger side streeting column, located near the fuse switches.
When active, the check engine light will constantly blink, and the radiator fans will cycle every second. This is tested on a USDM Subaru Impreza WRX 06+.
How to turn off Test Mode?
Disconnect the two green connectors and this is considered the standard connection status. So, if connected, disconnect before driving.
When do I need to connect?
If you are answering this question, then it's best to leave this connection unplugged.
The only reason to plug in these connectors is to reflash your ECU using tuning application that uses OBD II.
FAQ
Q: Do I need to connect the passenger side as well?
A: On my Subaru, the right side was already connected, stock.
Q: I don't see the green connectors?
A: If your Subaru is newer, you probably do not need it and can flash right away.
Q: My Subaru does not cycle like you say?
A: If this is the case, you might need an adapter to put your car into test mode.