[kil0ran]

So, in a year of riding with Di2 on the bike and at least a couple of tumbles I’d never had Di2 crash mode kick in – until this morning. Oddly triggered by slipping off the drive side pedal following a clip-in fail. Crash mode “docks” the rear mech to try to protect it from damage when hitting the deck.

Given that it isn’t well-documented and rarely encountered I thought I’d share some real-world experience.

1. You’ll get dumped into the small cog

2. The rear mech will still respond to the shift buttons, it just won’t move very far. A downshift might get you one cog lower but it won’t stay there. The fact it moves means that it isn’t a cable/power/motor failure. This is what fooled me as I’d assumed that crash mode meant power was cut to the rear mech.

3. Your front mech will still work and providing you can push a small/small gear combination the bike is completely rideable.

To get out of crash mode the manual says “press the button on the underside of the control box and spin the cranks”

If you’re like me you’ll probably have forgotten there is such a button.

When you press the button the rear mech springs back to life and in my case changed all the way down to the big ring. On reflection it probably would have been better to not do this when I was actually riding, although Di2 is more than capable of handling full-power shifts. 

Would be interesting to understand how it is triggered and what triggers it – its on my daily commuter and so is regularly chucked in the back of the car and has never triggered until now.

Topic

[Kerans]

Thanks for this guide, couple

Thanks for this guide, couple of corrections and a small extra bit that might help someone:

1. You need to hold the button on the junction box for 5 seconds until you get a flashing red light to enter crash recovery mode.
2. You should start spinning the cranks (bike upside down worked for me at the roadside) as soon as you get the flashing red light, the bike will shift onto each ring of the cassette (all the way up, all the way down) so keep spinning.
3. If after this your rear derailleur still does not work like me, check that during the crash you did not pull any cables out of the junction box. For me one of the cables was “out” but still in the hole. A little tug will dislodge any loose ones.
   The cables just click back into the junction box, you have to be quite firm.
4. For me I did not have a visibly bent hanger (I checked against the spare) but still needed to do the micro-adjustment to get things shifting smoothly:
   https://bettershifting.com/micro-adjust-your-road-bike-di2-rear-derailleur/

[Author]

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