Ok, Suzuki talks about a "special tool" to reveal the FI codes in the manual. The "special tool" is $15.99 from Suzuki. In reality it is a single toggle switch with two wire leads and probably a pin insert at each end.
The "special tool" works by using the two leads to connect two jumpers on a wire header with the 109.
I'm cheap and spoke to a local bike shop, P**** T***, and John told me all about the "special tool" when I asked him. I won't put the shop name in because I'm not sure if Suzuki police exist.
Ok, I have a "special tool", only $15.99, see pic below:
Here is the plug which uses the "special tool". Pull the left side cover off by the ECU, and there will be two unused plugs with black boots on them. One of the plugs inside the rubber boot is black and the other is white. Remove the boot from the white plug.
To keep perspective, rotate the white plug so that the plug 'lock' pin is on top. See the highlight in the picture below:
Then on the right side of the plug, you will insert your "special tool" into the top right pin connector hole and the bottom right pin connector hole.
Turn the bike ignition on - there is no need to start the bike. The FI code will display in the odometer box. C##. Look up our FI error code in the manual, or call Suzuki with the number, and then you'll know what's up with the FI.
Now, another tip about the FI code in the odometer box using the "special tool". When you look into the odometer box and see the code, e.g. C46 (EXCVA - exhaust control valve), just to the left of the code will be a hash mark. That represents the position of the throttle open percentage/position. If you then open up your throttle, the hash mark will move up screen to represent the increasing open position of the throttle. If it is moving appropriately, that is supposed to mean that your throttle is working ok.
That's it. That's all I know about this. Enjoy.