Re the Haldex/VAQ/LSD & the GTI-PP:-
Borg Warner who are the manufacturers of the unit, call it “Front Cross Differential Technology”, or “FXD”.
ERWIN, which is the official VAG workshop manuals, call it a “Front Differential Lock”, & in the “Self-study guides” they also refer to it as an “Electrohydraulic Front Differential Lock”.
Volkswagen Audi Group HQ in Germany, call it “Vorderachsquersperre” (VAQ), which translated from German to English means “Transversal Front Axle Locking”, or “Front Differential Lock” depending on the translation website used.
VW marketing who are not engineers & don’t talk to the engineering/mechanical depts. refer to it in the sales brochures as a “mechanical limited slip differential”.
Unfortunately, it is NOT a “mechanical limited slip differential”, & this has been the sole cause of huge amounts of misinformation & misunderstanding, all because they decided to “simplify & up-sell” the unit, thank you VW’s marketing dept.!
The VAQ unit is a highly modified Haldex unit which is fitted outside of the gearbox case & sits between the gearbox case & the driveshaft on the UK drivers side. It is an electro-hydraulic activated multi-plate clutch pack which locks up the existing "open" (basic) type differential in the gearbox case. It relies heavily on the data from the existing ABS/ASR/ESC sensors.
It can never be an "L.S.D.", as a Limited Slip Differential sits inside the gearbox case in place of your existing open/basic type differential. The term LSD has been around for decades since LSD's were invented.
Since 2013, in both the VW self-study guides & official workshop repair manuals, it has clearly stated that:- “The oil should be changed every 3 years regardless of the mileage”. The total quantity of oil in the FDL unit is 570ml +/– 30ml, the “change” quantity is approximately 0.4lt.
The electric pump which pumps the oil has had numerous failures, across all VAG brands & both applications, (FDL & AWD) as it’s the same pump part. This pump made for the Gen.V Borg Warner units might have just had a bad manufacturing batch, or a more serious design issue. It appears to be costing about £350 to fix if out of warranty