Your Shimano Di2 rear derailleur stopped working after a crash. This means that the electric motor has been disconnected from the Di2 system, preventing further shifting to minimize and protect the rear derailleur from damage.
Some cyclists refer to this lesser-known Di2 function as crash mode, while Shimano calls it the RD protection function.
What is RD protection function?
It’s a mechanism to protect the rear derailleur in the event of a crash or strong impact. Once activated, the rear derailleur will stop working temporarily.
How do I know if the RD protection function is on?
The rear derailleur stopped working immediately after a crash or if you’ve hit a pothole or uneven road hard.
How to reset the RD protection function?
Before you reset the RD protection mode, make sure to visually inspect the rear derailleur and hanger to ensure they’re not damaged.
For 10-speed and 11-speed Shimano Di2
This applies to 10-speed (R7970 / R6770) 11-speed (R9150 / R9000 / R8000 / R6870) and 10-speed Shimano Di2 rear derailleurs.
To reset the RD protection function,
- Lift the rear wheel.
- Press and hold the button on Junction A for five seconds until you see a blinking red light.
- Turn the pedals slowly, and the rear derailleur will automatically shift through all the gears to reconnect the motor.
- Continue turning the pedals until the shifting completes.
For 12-speed Shimano Di2
This applies to 12-speed R9200 / R8100) Shimano Di2 rear derailleurs.
The 12-speed rear derailleur has a different design from its predecessors and doesn’t require you to press the reset button.
According to Shimano,
While turning the front chainwheel, operate the shift switch until the gear is shifted from the largest sprocket to the smallest sprocket.
In other words, continue pedaling while shifting to the largest cog, then all the way to the smallest cog. This will turn off the RD protection mode, and the rear derailleur should function normally again.