My FLSTSE2 Electrical Diagnostic Manual (PN 99498-11A), page 2-1, says Trouble Codes can be retrieved through the Odometer self-diagnostics:
".... press and hold the Trip odometer reset switch located on the left handlebar controls, while turning the IGN ON".
When you release the trip odometer reset switch, "diag" will appear on the odometer display.
Press and release the trip odometer reset switch. ECM will appear on the odometer display. It will have either a "Y" or a "N" after it, depending on whether there are any ECM codes or not. Quickly press and release the trip odometer reset switch to cycle through the other modules - BCM, SPDO, and ABS. When the desired module is displayed, press and hold the tripmodometer reset switch to display any Diagnostic Trouble Codes stored in the module.
The instructions in my manual for ending the process don't work on my bike, so I just turn off the Ignition.
Hope this helps.
Regards