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I've been chasing this ghost for a past 2 weeks now. I own a road bike with Ultegra di2 and rear shifting stopped working (kind of) 2 weeks ago. You press lever, lights on junction box illuminates indicating battery life left, but nothing happens. I started charging it, afterwards it didn't work but then randomly it started to shift like nothing is wrong. I rode 100km in the evening, went to sleep, woke up the next day- doesn't shift once again.

At this point I call my mechanic and schedule an appointment, I put my bike in my car, drive there, take it out, bring it to a shop, I start telling what is the problem and it shifts. I click like 10 more times and it shifts flawlessly. Guy looks at me like wtf, but we agree to keep bike at his shop for a day, maybe it will stop working. Spoiler alert- it didn't, worked all day, I bring it back home, ride another 80kms on it, go to sleep, next day it doesn't work anymore.

Anyone seen something like this? It seems that it stops working only if you leave it unattended for like 2+ hours. If you keep it in the room and keep fiddling with shifters once every couple of minutes- it never fails. I've been away for the past 3 days and I left it not working, I came back today and it still didn't work, but I cycled like 7kms with a single gear to my friend's house, moved my saddle and pedals onto his spare bike and boom, my bike started to shift. After 2 hours bike ride once we came back, it was not working once again. I put it in a car- it works again. WTF?

Like a month ago, I had a crash in a race, I fell on right side and broke off rear derailleur hanger, I got it changed. Battery was replaced ~year ago.

If it doesn't work and I connect it to Etube, it recognises every component including rear derailleur, although I don't have sufficient cable to run error checks. Well at least I cannot do that, you click on error check and nothing happens.

At this point in time I am a little bit desperate. I cannot take it to mechanic, because after car ride it starts working out of the blue.

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    I'd be trying to hunt down a loose connection in any case of an intermittent fault, especially with Di2, which is a little probe to losing contact when the cables are stressed (perhaps due to your crash). I'm sure this is a duplicate of a question with several answers. I'll have a look when I get a chance
    – Chris H
    Jul 3, 2022 at 20:06

4 Answers 4

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I can't comment about Di2, but when the symptoms you describe arise in an electronic circuit between two boards, there is seldom anything wrong with the boards. The problem is invariably a poor connection.

With time dust slowly makes its way between surfaces at connections that are neither soldered nor bolted, introducing a discontinuity or a high resistance.

The solution is surprisingly simple. Just pull out each connection and re-insert it five or six times. The two surfaces will act as mild sandpaper against each other, re-establishing contact. If you spot dust accumulating at the surfaces, that might be a sign that the connection is not sealed well enough—and, unless you solve that problem, the process will likely need repeating. It appears though that you will be unable to see the metal—at least on one side of the connection (EW-SD50; EW-SD300).

In other words, ChrisH's and Noise's diagnoses are correct, but it's unlikely that having an extra loop affects the connection, as turning the handlebar presumably doesn't tug on the cable.

If you can spot two exposed points from which to debug the problem using an Ohmmeter, that would be simplest. (Did Shimano anticipate this sort of common-tools diagnosis by providing exposed connections at either end?)

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  • Electrical Contact Cleaner dripped/sprayed into the connector may help too "de-oxit" is a brand, but there are many.
    – Criggie
    Nov 17, 2022 at 21:23
  • @Criggie I'm guessing the two sides are gold-plated, and that oxydation would not be an issue. The nice thing about rubbing the two very surfaces that you want to connect against each other is that they build micro-grooves in each other and somehow mate very well afterwards into a better connection.
    – Sam7919
    Nov 17, 2022 at 21:55
  • @Criggie ... and then maybe they're not gold-plated after all, or at least the term 'gold' doesn't appear in the various documents.
    – Sam7919
    Nov 17, 2022 at 21:57
  • yeah - sweat does damage to most electronics over time, and depending on location it could be vulnerable. One would think Shimano would design for this kind of thing, but I'm also cynical
    – Criggie
    Nov 17, 2022 at 22:00
  • @Criggie I need to be careful. I dissed SRAM (hydraulic brakes) recently and that was alright, but when I dissed Shimano (cranks), many were indignant.
    – Sam7919
    Nov 17, 2022 at 23:35
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The last time I saw this type of problem (intermittent front shifting), it was due to a poor connection at the shifter. Shimano say the cable at the brifter should have a little loop to relieve stress but this bike had the cables basically taut behind the bar tape and after a bump (minor crash), it was loose enough to work only sometimes, just like yours.

It could also be an internal problem from crash damage.

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This same thing continues to happen to me. I thought it was the battery, so I bought a new battery. That wasn't it. The LBS found that one of the wire channels was not working, I am told there are 3, they moved the harness to channel #2 and it works. Except sometimes it doesn't. About once every 2 weeks it just stops working. I was on mile 22 yesterday and I had to ask my group to give me a minute. I pulled the battery and then touched the harness and it came back. It took the bike shop 3 weeks to figure it out. They ordered new derailers but that was not the issue etc... Very hard to figure out the issue if they don't know how to fix it. When everybody moves over to electronic shifting next year maybe the shops will get better at diagnosing these issues. Over the winter I am going to ask them to yank the internal wiring and replace it. I can't be 30 miles out & get stuck with one gear for the return ride.

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    Hi, welcome to bicycles. It doesn't sound like you've actually figured out what the answer is yet, though, so it's probably better to wait until you can answer the question. As it is, this is really more of a comment. You might want to take the tour.
    – DavidW
    Oct 17, 2022 at 22:06
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Good afternoon

I have a similar issue but I had no crash. Since saturday my Shimano DI2 Ultegra 12-speed has been weird, suddenly after 3 hours riding it stopped working, I could not shift anymore. pressing the RD button did not help, no lights went on, my friend with the same DI2 pulled out his shifting cable and put it in my RD and then the light went blue, I did my shifting cable in but no light. Then I thought it was the battery but I charged it a week ago so I was sure it was fully charged, back hom after riding on one gear I put in the charging cable and directly it went blue and everything worked again, so it just got a sort of power pulse from my charger and it was all ok. Then I connected with E-tube app and I could see as I thought all batteries of the shifters and baatery in seatpost are completely full. The on Sunday morning also after a few hours and I was glad I was almost home it stopped working again, now I had my powerbank with charging cable with me, so I put the cable in for a few seconds and the light went on again and it worked. What is the issue here? Is it my battery which has a memory fault/leak or do I have to search further? Thanks in advance.

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  • Hi, welcome to bicycles. It sounds like you want to ask a question of your own, so you should post this as a question instead of as an answer.
    – DavidW
    Aug 29, 2023 at 14:38

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