Haldex questions


Registered User
I'm trying to make my haldex engage from my phone (since my controller is dead) for this I'm using a stepper motor driver, an esp8266 and a buck converter.
After reading the document at:
I've got some questions on the function of the haldex controller.

According to the picture 1 the regulator pin has to only close the lower oil gallery to obtain full pressure on the clutch. So i made it work exactly like that, in my setup the pin only reaches the top on the lower hole (closest to the motor) see picture 2 and video 1, however, after installing the new modified controller the awd doesn't work, it's completely off. I am sure that my setup is working because i can hear the motor engaging and disengaging when i press the button on my phone.

Can someone tell me how high the pin has to reach? is it at the top on the lower hole or it has to close all the holes?

My initial idea was that there was not enough oil pressure in the haldex to engage the clutch (because in my setup the pre-charge pump never engages) but in the document it's said :

Function When a speed difference is present between the input and output shafts, the input shaft, together with the roller bearing of the lifting piston, rotates around the still stationary lifting plate of the output shaft. The roller bearing of the lifting piston tracks along the undulating surface of the lifting plate. The roller transfers these upward and downward movements to the lifting piston, causing it to perform a lift movement, building up oil pressure.

After the engine has been started, the pump for the Haldex coupling is supplied with voltage by Haldex control module J492 as soon as engine speed exceeds 400 rpm.


The pump for the Haldex clutch conveys oil to the lifting piston and brings the lifting piston into contact with the lifting plate via roller bearings.

At the same time, oil reaches the working piston. This eliminates any play from the clutch plate set and ensures quick clutch response.

A speed difference between the propshaft and the internal shaft builds up oil pressure, the precharge pump in only there to buildup initial pressure to make the haldex engage faster (as it will only be powered on only once)

In my case i made the front wheel spin for about 2 mins (which should be enough time to build up oil pressure), and engaged the haldex with my phone but no AWD.

Do i need to activate the precharge pump once the car turns on or it's useless since oil pressure will still buildup when a speed difference occurs?

Thanks for reading!

Picture 1:


Picture 2:

Video 1:


Registered User

I removed the controller and it turns out that the pin can't physically reach the top hole because the spring is already compressed too much and it's in the way, so my guess is that the precharge pump needs to engage when starting the car?


Registered User

After bench testing the unit i figured out how it works so now i have working AWD controllable from my phone. However as i pulled out all the original electronics from the controller I get an ESP light and the ESP doesn't work, an error in ABS brakes j492-no communication.

Is there any way to code out the Haldex from my ecu so i get the ESP functionality back? I have an original VAG com cable.