Maybe you should post in the G20 forum how to pull the codes.
IF its the same as the B14, here is what you do.
You'll need to unbolt the ECU the first time you do it. On the back there is a place for a flathead screwdriver to turn something.
Put the key in the ignition and turn it to on, but dont start the car.
Use a flathead screwdriver to fully turn the screw on the back of the ecu. Wait 5 seconds. Fully turn it back. Look at your check engine light. It should be flashing. Record the number of long and short flashes and ask the G20 forum what they mean. Now turn the screw in the back of the ECU again, wait 5 seconds, turn it back. Remove key, you're done.