When Shimano introduced Synchronized shifting june 2016 they also changed the behaviour of the Junction A. When you check the Di2 battery level the LEDs on your junction box will first indicate the battery level, turn off and then illuminate again to indicate the selected synchro-shift mode. The different modes are:
- Red and green LEDs turn on for two seconds – manual shift
- Red and green blink two times – synchronized shift mode 1
- Red and green blink three times – synchronized shift mode 2
Has your bike suddenly started doing this, even though you’ve had it for a long time? Your junction A firmware has probably been updated by either you or your local bike shop.
Note that this behavior will always trigger when you check the battery level, even if your bike doesn’t support synchronized shifting.
(provided your firmware is up-to-date)