PETG seems to be quite “sticky” and doesn’t seem to clean off the way PLA and ABS do… instead of peeling off of the nozzle on the cleaning pad, the PETG seems to just end up smearing all over the tip.
The trick I’ve found is to ensure that the nozzle is thoroughly clean manually, before letting the firmware run the cleaning/probing sequence.
a) Ensure that the tool head is pre-heated, and once at temp, retract a few mm of filament. Skip this step if you’ve just completed a print, because the stock firmware has already retracted the filament a bit. This helps to lessen the chance of filament oozing out.
b) Pre-heat the extruder to the cleaning temperature.
c) Use the tweezers to “snip” off any filament that you can, being very careful to avoid the block and those wires (!).
d) Use a scotch-brite pad (non-metallic) to scrub off the tip of the nozzle. I use the tweezers as a “feeler” to assess the cleanliness of that tip; you can generally feel the difference between a small layer of softened PETG vs the brass nozzle. Again, use care to avoid the wires on the block.
e) Repeat © and (d), until you’re quite sure that it’s clean.
f) Start the print, keeping a close watch on the probe sequence, and abort it (and redo this procedure from (a)) if there’s any visible bounce on the washers when the nozzle retracts from the probe point.
Using this strategy, I’ve had nary a single bed leveling failure with any of the PETG and T-Glase prints I’ve done.