Idler cannot home #04125 (MMU)

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What happened?

Before it can align with any of the filament positions, the Idler inside the MMU unit needs to be “homed” to determine its position. First, the Idler moves to one end of the travel (endstop). Then, it moves to the other endstop, while measuring the angle between the end stops. The idler homes after the unit starts up has been reset or after another error occurred.

In case it can’t find the first homing endstop or the distance between the two endstops differs from the expected value, the printer will show an error. 

Distance between the Idler endstops: 225 degrees 
Allowed deviation: 10 degrees

How to fix it?

The issue is usually mechanical. If you get this error, check the following items:

• Verify there is no debris around the Idler and that it can move freely.
• Release the idler tension screws slightly. If it is too tight, it will disable the Idler from moving freely.

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• Verify is the Idler Coupler is attached properly. Check both grub screws on the Idler Coupler are tightened and that one of the screws is facing the flat part of the motor shaft. Make sure the Idler doesn’t push against the Idler body so that it can rotate freely.

• Especially the first time you are running the MMU, check that the motors are connected in the correct order.
• Verify all the bearings can move freely and that the center shaft at the end is inserted into the Idler properly.
• In some very specific cases or on modified units or in other unsupported setups; changing the stall guard thresholds might help.
• In case you are using the older MMU2S unit, check the MMU idler unable to move freely article.