Just thought I'd share my recent experience with this problem.

2009 (09) Jaguar X-Type 2.2 Diesel Automatic 112,000 miles

Car going into limp home mode on foot flat down on accelerator.

Coil light illuminates on dashboard

'Gearbox fault' on dashboard

Limp home mode

Turn ignition off, 5 seconds, restart, fault clears

Repeat above

I took it to a local garage who replaced the EGR

Drove fine for a week then same fault

Replaced Diesel fuel filter

Drove fine for a week then same fault

Replaced Air Filter

Drove fine for a week then same fault

Garage suggested Gearbox or gearbox sensor was faulty

I then went on ebay and bought 2 tins of Turbo cleaning spray for £20 and 2 bottles of diesel additive for £30

Spraying the turbo cleaner into the turbo which was ridiculously easy and put 2 bottles of Wynns Diesel Clean (Extreme Cleaner) 500ml and filled the tank.

Drove at 70 MPH until the tank was empty and ....

PROBLEM SORTED and it drive beautifully with less engine knocking too.

Hope this helps some people on the here with the same issue.