Loosen the bolts in a crisscross pattern in several steps, then remove the final driven gear (A) from the differential carrier (B).

Install the final driven gear with the chamfer on the inside diameter facing the carrier. Tighten the bolts in a crisscross pattern in several steps.
Honda Fit 2007-2025 Navigation Online Reference Manual
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Secondary HO2S Replacement
Special Tools Required
O2 Sensor Wrench Snap-on S6176 or equivalent, commercially available
Disconnect the secondary HO2S connector (A).
Raise the vehicle on a lift.
...
Fuse Locations
INTERIOR FUSE BOX
UNDER-HOOD FUSE BOXES
Primary Fuse Box
Secondary Fuse Box (On the battery)
...