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Discussion Starter #1 (Edited)
Long story short, my 2008 Smart Fortwo I had recently purchased would occasionally throw 3 bars, usually shortly after starting it and typically when shifting into drive, but not always. Sometimes it would throw 3 bars from the start, sometimes it would go a few days, even a few weeks one time, without any issues at all. When it would throw the 3 bars I could re-train it a few times and it would sometimes be fine all day, sometimes it'd throw 3 bars a mile down the road then one more retrain and it'd be fine for the rest of the drive. Frustrating would be an understatement.

Codes I got (these did not show up for a basic ODBII scan, need something that talks canbus)

Module "N15/6" (Sprintshift Control Module)
P0707 - Signals from incremental sensor of component M17 (gear motor) are unreasonable
P1800 - Transmission teach-in was required
P1801 - Teach-in of mechanism not successful
Module "N47-5" ESP control
C1301 - short or open circuit of CAN wires

I did all the usual things, looked for shorts (especially considering the C1301 error) and found nothing. I was pretty sure the issue was with the shiftmotors, so I started figuring out how to get to it. I note here that I posted this at clubsmartcar.com at the time and am reposting much of that here to be of use for members here. There was input and suggestions from others, there and elsewhere to help as I went, community payback is part of the motivation for posting here.

The TL;DR here is I replaced the shift motors, for everyone else....

It seemed easiest to get to the shift motors from up top, but the airbox is is in the way. It was not terribly intuitive where the bolts were, I marked them here with red arrows. The one on the right I did not remove and instead channeled the powers of my alter-ego, DumbStrong, and broke the plastic mount. Whomever approved putting that bolt in like that earned my ire; due to the angle it seems to me the only way to get to it is to drop the subframe. Breaking the mount didn't harm much, so whatever.
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Once the airbox was out of hte way, I felt I had a chance of actually getting this done. Here's a shot with the airbox out of the way.
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At the top of the shift motors, you can see some dark stains; I believe this is from fluid/vapor coming out of the vent and settling there. The top two bolts might look crusty, but they were shiny new compared to the bottom two.
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It took me a while to figure out how to remove the plugs, eventually I got some images which showed the tab on the front and with a bit of jggery pokery figured it out. I slipped a small screwdriver in from the face of the plug, below the tab in the center and gently lifted the tab up and it came apart easy. The arrow in the pic with the plug shows where I inserted the screwdriver.
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And a shot of the crappy bottom bolts. You might not think it, but some penetrating oil, a day to soak, and the torx cleaned out well enough to remove them.
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Discussion Starter #2 (Edited)
At this point I could pull the shift motors off. Here's a pic of the underside of the assembly. Note the crud on the gears, that's lithium grease the PO squirted in there in the hope it would fix the problem, obviously it did not.
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And here's the the transmission side of the mount. Note the gunk on the left side near the gears, that's some more lithium grease down in the transmission, ugh.
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It was at this point I put a another set of shift motors on there, put everything back together and the car has been flawless ever since, but what's the fun in that?
 

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Discussion Starter #3 (Edited)
There's an electric motor on each side of the assembly, under the steel cap on the ends, each one drives the shifting gear on it's side. 2 bolts hold each cap in place and this is the outer casing of the motor itself, it holds the permanent magnets and one of the bearings. I removed it carefully to prevent the magnet from pulling things out of control and damaging the magnets, windings, shaft, etc.

Under it I found this travesty.
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All that black grit is carbon from the motor brushes. You could say the brushes were gone, but no, they're still there only not in brush form anymore. :p

After a little cleanup of the loosest crud....from here on out it'll be mostly images that tell their own story.

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This was the carbon crud that I came off one motor easily, there was still much, much more.
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And some post-cleanup images, you can see the brushes are worn down to mere nubs and the bearings were worn well outside of tolerance. I think replacing the brushes and bearings should yield a serviceable set of shift motors, it's on my TODO list, just not much of a priority.

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There you go. If you ever wondered what's in there, now you have a glimpse.

Edit: all the typos!
 

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Good job, two years ago I changed my gear oil with Redline MT90 and just as a normal maintenance I disassembled the shift motors and cleaned them...
I had carbon inside but not like you. I filled the new gear oil from the opening:

IMG_5346.JPG

This made the gear oil change quite easy...
 

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...nice write up...and now you can see why removing the white cap and spraying Lithium grease down the opening does nothing to the motors and just contaminates the system...
...the two gears in the tranny side have a triangular marking on them....line them up side by side and place them facing straight up...it will help getting the motors in sync and minimize learning time...

Jetfuel...BTDT
 

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Discussion Starter #7
...nice write up...and now you can see why removing the white cap and spraying Lithium grease down the opening does nothing to the motors and just contaminates the system...
...the two gears in the tranny side have a triangular marking on them....line them up side by side and place them facing straight up...it will help getting the motors in sync and minimize learning time...

Jetfuel...BTDT
Good point which I had all but forgotten about. Since I was swapping shift motors I oriented the new ones to be in the same alignment as the old ones, easy enough just find the triangle on the shift motors, count teeth until you are parallel with the housing. Rotate the wheels on the replacement to the same position and put it in place. I did not test what would happen if one doesn't do this, but I didn't have to go through a reteach to get it started. Might be unnecessary voodoo, but that's what I did.
 
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