2002 Jaguar X type and it's giving me a gearbox fault code what is this I am not really experiencing any problems?

Is it an automatic? There is no dipstick as transmission is sealed. If you remove battery then on top of trans is Allen screw. If you pull drain plug on bottom of pan then you should dump 7 quarts fluid. Add new fluid (Advance Auto knows what kind it is nothing special just old Dex III Mercon) via Allen plug on top.

Look - by the time I added fluid I was short 3 quarts and the trans was shifting hard into 3rd (solenoid sticking). You have no method to avoid over fill as there is no dip stick. The old "add fluid until you see it in the hole" will overfill for sure. Then you will leak all over the place.

I drained and then topped off with 7 quarts store brand and ran for a few hundred miles to flush. The sticky solenoid got WORSE. I drained the dirty and added 7 quarts Castrol with the $10 Lucas stuff and I am thrilled! No more sticking solenoids, trans shifts great, and no mystery about the Jap transmission.

Fancy synthetic fluids are great, however, I got great solution to my issue right now. The only reason to use "special" trans fluid is if you want to forget about it. And if you own a Jag then you know that maintenance is something you better get used to.

Oh and the X has 135,000 miles and still running strong!