Di2 rear mech one gear out of phase.

My Di2 rear mech thinks it is one gear higher than it actually is.

It wants to shift into a larger sprocket that isn't there, so would go into the spokes if I didn't have the limit set in. And it won't go into the smallest sprocket.

When I hook it up to e-tube it confirms this - eg when it is actually in the 4th biggest sprocket, the software says it is in the 5th biggest.

The problem came about after I broke my hanger in November. I changed it, and put the bike on the turbo and thought something was odd but didn't need all the gears on turbo so didn't look at it, until yesterday I got the bike ready to ride and realised there was an issue.

I've just changed the Hanger again and it is still the same, one gear out of phase.

I can't see any way to reset it in the software. There aren't enough trimming 'clicks' available to shift it fully to the right gear. It's like I need to reboot the mech but can't see how.

Anyone come across this? When I Google it I mostly get people saying it's the hanger, but I've changed the hanger twice and it hasn't helped.

It's ultegra 6870.

Normally you set the limits and then doing the trimming while in a middle cog - are you doing that? If the limits are too far in, then it's "middle" will be off and you'll be out of trim range.

Setup steps: https://assets.bettershifting.com/di2_dealer_manual_ultegra_6870_8e8227ec85.pdf

Shimano say 5th cog. Mine's not been far enough off that I've taken note which one I used.

I had this with my old Mason Bokeh.
There was a slight difference between the hanger for a mechanical rear mech and a Di2 version. No idea what it was.
Might be the case with yours too?

Yes, I followed those instructions. It indexes perfectly, just it won't go into the smallest sprocket because there isn't another click. But there is an extra click when it is already on the large sprocket, so it needs the lower limit set well in to keep it out of the spokes.

I didn't know that there was a limit to the number of clicks, but there is, there are just enough for the number of gears, so there isn't another one for me to get it into the 11T.

Given it's my ultra bike I can live without the 11T so not the end of the world, but weird.

Interesting. How did you fix it?

Mine has only ever had Di2 on it.

I stuck a new mech hanger on mine.
It originally had mechanical but was upgraded to Di2 later on. If yours has always been Di2 it doesn’t sound like the same issue.
Only other things I can think of is a bent hanger or limit screws out of adjustment.

OK, thanks, glad you got it sorted.
It would need to be two new hangers bent in the same way, so unlikely but not impossible. And it doesn't shift to within an entire gear of the upper limit, so I don't think it's that either!
The search goes on...

Sounds like you need a thicker hanger
It didn't happen before you changed the hanger initially right? So have you bought the wrong one? Twice

Put a washer between mech and hanger?

Can relax the high limit screw so the mech goes into the highest gear? Has the mech trim setting been set too far in?

I’d always look to get the high limit set first, then move to lowest gear and set low limit. Finally do any trim to perfect the indexing.

Yes, that would fix it. A 4.35mm washer and it would be perfect. A bit of a workaround though, would need a longer bolt. And a longer skewer.

It's not reaching the high limit, it won't even reach the smallest sprocket.
I tried backing off the limit but it doesn't change anything. It's not the limit which is stopping it, it's its belief that there isn't another gear there / lack of the final click.

I'm pretty certain it's a software fault rather than hardware. Maybe I need to get on to shimano. Well out of warranty though.

I had something like this a while ago. Check that the trimming is in the middle and not trimmed so far to one side that it's in the next gear. Doing the factory/crash reset procedure set the trim back to the middle and I was able to reach all the gears again. Worth a try.

I asked about the trim a couple of posts back.

Was gonna state the obvious and tell you to follow religiously the dealer's manual (starting at p.64), but @hippy already covered that.
Have you tried taking advantage of that and go into adjustment mode when you're on the 6th sprocket then? Might offset the whole thing (without fixing the root of the problem, but hey ;)

Also, I think I experienced something vaguely similar when setting mine up (but it's been so long I can't remember exactly what it was), and I think it had to do with the trim being offset : when the derailleur was on the fifth sprocket, I had alread used all of the 16 adjustments steps. I don't remember how I fixed it unfortunately, not sure what can be done to reset it except the standard "after crash" procedure, as @Matt101 is suggesting.

Do you want to borrow my hanger straightener tool just to make sure the hanger is aligned? If you bent a hanger though, you could also have bent the derailler itself so what I'd do is test the hanger alignment is ok, if it is, swap in another RD and see if that works across the whole range (I've got a couple of Ultegra ones you could use). If that works and the borked RD with the limit screws wound out doesn't work then it's probably a bent RD.

That's an interesting point.
I had forgotten this but I have also changed the cage plates as I thought they had got slightly bent when the mech got ripped off and old hanger snapped (when I had them off they didn't actually seem bent). So its kind of a new mech that has never worked properly. It's possible I didn't put the new plates on right, or the mech got bent somewhere else than the cage.
It could be good to borrow one of your mechs if you have a spare to see if that works. I expect it would but good to check.
Also Hanger alignment. I was ruling this out on the basis that I've put two new hangers on with the same result but the (carbon) frame could have got slightly bent at the dropout when the mech was ripped off.
I'll look into crash mode first then come back to you, as that will be easiest and I would like to understand it better.

If it is either bent mech or the hanger alignment it still shifts perfectly over 10 / 11 gears. Did audax on Saturday with no shift issues all day. Makes me think it is more likely to be software, but not impossible.

Thanks, it's not trimming as I have trimmed it as far as it will go and it's not enough.

When you have it wired up to e tube it tells you what trim position you are in and you can adjust it on the computer (I didn't know you could do all this until last weekend).

But I messaged LBS last night and his suggestion was it might be something to do with crash protection. I'll see if I can trigger crash protection and if that might reset it.

Generally I've found with bent stuff you get odd shifting in a couple of cogs changes. But it's possible you bent it evenly enough (or messed up the cage swap in some way - wrong part? missed a washer?) that has evenly pushed the whole cage too far in one direction.

I've got to go to the dentist today, over your way. The Mason is currently in bits so I could bring you the RD off it (but I'll need it back soon). It's probably not perfect (I dropped it a couple of times) but it definitely shifts into all cogs on my bike so would be a good test.

Are you around today? Depends how the dentist visit goes but I could come over later or this eve and have a proper go at it.

Yes, sure - if you're passing. Would be a quick test.
Thanks.
I'm around all day apart from picking up daughter around 6.
Good luck with dentist!

Anyone know how I could get my mech into (not out of) crash protection mode without me hurting myself or risking knackering the bike?

Yes, but if it's changing gears, it's not in crash protection mode.

Wait, you want to put it in CPM or get it out of CPM?

Get bike in stand with rear wheel off ground, then hold down the di2 button for 5 seconds while spinning pedals forwards. This will reset. It'll run through all the gears, hence needing to keep pedals spinning

I want to get it into CPM.

I have a hunch that it went into it when it got ripped off, and didn't reset properly.