Vorderachsquersperre, VAQ System, Ediff, ELSD
The front E-Diff fitted to the Golf GTI and Seat Leon Cupra system is based on Generation 5 Haldex.
It is given many names – VAQ system, Vorderachsquersperre (German for “transverse front axle locking”), Ediff or ELSD. But as complicated as this may sound it is nothing more than a Haldex type clutch pack which locks the rotation of the left wheel to the right (and thus the right to the left), it stops either front wheel spinning by locking the diff. It clamps the non gripping spinning wheel over to the non spinning wheel. There is still a normal diff in the final drive of the gearbox, then this E-diff transfer box slips into the right hand side of the gearbox where it meshes into the middle of the normal diff just like a drive shaft would, then it has another spline on the outer tube which meshes into the diffs outer housing thus the final drive (see picture below). The system simply clamps the right prop shaft output onto the outer final drive casting of the diff, thus it stops the diff from differentiating, thus acting like a controllable diff locker.
The system uses the ESP/ABS module to monitor wheel speeds, then if there is demand for torque/power from the driver the ESP system watches for wheel spin by the ABS wheel speeds sensors and if there is an excessive speed from either front wheel then it locks the diff together. This is not a simple crude engaged/disengaged system, instead by varying the pump motor speed it varies the clamping pressure of the clutch plates thus it controls the torque applied or slippage as its sees fit.
Everything about the VAQ E-diff is Generation 5 Haldex – the pump, the control unit, and the clutch basket design. There is the same type of piston assembly and brass pressure relief valve. Here on this page are some photos of a strip down so you can see for yourself.
Being a Gen 5 Haldex system it has the same issues as comes with Golf R, Tiguan etc MQB platform Gen 5 Haldex vehicles, e.g. the gauze blocks up, the motor fails, and many people never notice that it isn’t working. The difference in construction is these have a proper sump chamber in an alloy box on the side, with both the fill and drain bungs. But as you can see from the internal design (click on picture to the right below to see the sump inside), when you remove the drain bung, the bottom 10mm of fluid with all the clutch pack gunge material is stuck in there so really you need to take this little sump off and clean it out to do a job actually worth doing.
Removing the pump and cleaning the gauze is also important as always, and if you are looking for a guide on servicing, it would be a good idea to work around 20k miles or 2 years, and maybe more depending on how you use the car, as the more you apply friction though the clutch plates then the more scum will build up to clog it up. A track car really needs doing every 2,000 miles.
The control module can be accessed with VAGCOM VCDS under the module number 32 “Differential Locks”, the control module has the part number 0cq907554E and is called Quersperre. It has the same requirement for learning the pump motor as the Gen 5 Haldex system, so ensure after any repair or servicing of the diff that the pump learn is carried out which is documented at the bottom of this page, otherwise the motor will not operate correctly.
If you are getting fault codes such as 16671 or 16670 or 16668, which are often read as C111207 or C1112-07 or C111204 or C1112-04 then most likely your pump has failed and should be replaced, AND the pump learn function completed successfully. If you are getting 16670 or C111307 or C1113-07 you might be lucky as a clean out of the gauze, fresh oil and a pump learn might resolve it, otherwise you will be replacing the pump too. The pump you require for this system is part number 0CQ525549 (see below) and the oil you will need is Febi Bilstein 850ml Haldex Oil which you can also find below: