I have a 2009 XF and I just changed the transmission oil pan and transmission wire harness gasket. I thought the pan was leaking but it turned out that it was the harness gasket. I had the oil drained for a a few days because I couldn’t get the white tab back in to get the pan back on. Finally got the tab pushed in and filled with atf and closed up. I have not put the splash guard back on so I can make sure there’s no leak. I got mar car as level as possible when refilling. Today I was driving and got a “gearbox fault code”, but didn’t notice any issue. I took home and parked it. Any ideas why that code came on? Could it be I put too much or not enough fluid?

 

Quite possibly, these transmissions are quite sensitive to at least being under-filled, and probably overfilled too, which is why it's so galling that the refill procedure is such a pain in the ***! Speaking of, did you follow the official ZF/JLR proceedure?

Attached...

 

Check to see if you see a transmission performance code in the diagnostic or solenoid code. I had my 09 XF transmission replaced with a used one with low mileage on. The internals parts wore out and had to be fixed. I was driving with the gearbox fault for months until I had to replace it. Now it drives like new. Also check your rear diff fluid and parts if theyre still holding up. Had that replaced too. Engine still working like a young bull!

 

How is the battery looking? If you've not driven much recently then battery could be low and That can give spurious faults. Would ensure it's fully charged as many people are not driving much with covid and having battery drain issues