Hi Guys I have an Audi S3 race car and have been trying to figure out a way to control the Haldex manually. This quest has led me on a merry dance from various new controllers like HPA to SQA etc etc all are no good simply because I am using a GEN4 unit and a MOTEC ecu. Anyway I gave up and tried to learn as much about how the unit works myself and then got in touch with an electronics company to get them to make my own controller. They specialise in custom made stepper motor control units. We have basically figured out that on my GEN 4 unit I have a oil pump to create pressure and a solenoid valve to direct that pressure to the clutch pack or not depending on the valves position. Now dont forget this is a race car so my proposed system is as follows Switch on for pump to give me pressure in the system (pump now spinning) Rotary knob to manually set the solenoid position in a fixed position Button on my steering wheel to engage or disenage So at race start I have the system on and the knob set launch and I have AWD and get away nice leave on for first few corners to help warm the tires up Turn off (disengage valve) with my steering wheel buttton so as not to stress the plates too much Turn back on for those tricky overtakes All of the above is dooable with some electronics which they can easily do (They make WAY more compex system than this) But it has led to a couple of questions from him which are below. Hi Mark Weâve powered the solenoid up and from what we can see â (please correct me if Iâm wrong). The solenoid valve seems to sit with no power on it, roughly in the middle of the movement. â¢ If you energise it one way, the valve moves out about 2mm. â¢ If you energise it the other way â the valve moves further in, about 2mm. Weâve been through the PDF documentation on GEN 4, and whilst it explains what it does itâs vague about how it does it and how itâs supposed to work. Are you supposed to be able to move the solenoid in two directions or does the action of mounting it to the rest of the assembly, force the solenoid fully in or fully out â which then means you can move it one way only? The reason I ask this, is that itâs pretty simple to design a PWM style circuit to drive a solenoid in one direction â you vary the on time of the signal driving it, and assuming itâs pushing against a spring, the amount of on time gives you a rough idea of how far out it is (I stress rough, as it is not as accurate as the stepper design on the older haldex unit). However â if you need to move it in two directions, the circuitry gets a whole lot more complicated â as you need to incorporate an H-bridge style controller as well (to change which side of the solenoid is positive). The unit takes about 4A of power at 12V. let me know your thoughts so we can proceed with development Do any of you have the answers to his questions because I dont? I do not know if when the valave is mounted it sits in the middle of its travel or is one way or the other. Cheers Mark.