What exactly is your problem?
Replacing the Haldex controller for a known working replacement cured my issue.
I had a fault with my Haldex system where it was engaging permanent 4WD (max clamping pressure on the clutch pack within the diff), which results in crap economy, and bunny hopping / scraping / dragging the inside rear wheels during tight turns. All garages I took it to were at a loss.
Try pulling fuse 31. That disables the Haldex so by doing that your car will operate in front wheel drive. If that occurs, then you know that your diff and clutch is working fine because you’ve changed from 4WD to 2WD. So based on that, I assumed I had an electrical fault rather than a mechanical fault with the clutch pack. So I changed the wiring harness from diff to Haldex (no change with fault) so then I changed the Haldex controller for a known working used part and that fixed the quattro system so now it engages and disengages at the right times and works perfectly. VCDS wasn’t really useful in diagnosing the fault, but I could hear the pump whirring during output tests so I assumed that was still good. I have since replaced the pump as a preventative measure but it was totally not part of the fault in my instance.
Haldex controllers for gen1 (mk1 A3Q and S3) can no longer be bought brand new and nobody refurbishes them. It’s either too difficult or not worth doing. I’ve spoken to several experts about it. Your best bet is to buy a known working controller IF you suspect it’s the cause of your fault.
Sorry if I’ve repeated loads of stuff already mentioned in the thread but just posting my experience and what I did to cure the problem.
hi Mad_Dude,
sorry for the late reply was doing a bit more testing as i have only just got a fully licenced VCDS still learning how to use it. Having the same problems as you described. unplugging the haldex makes the problem go away, do not have fust 31 as pre face lift. my pump is whirring on output tests.
have had 2 intermittent faults:
00526 - brake light switch.
01324 - control module for all wheel drive no communication.
also cleared faults that have not come back:
01312 powertrain data bus faulty.
01316 - intermittent.
01314 - intermittent.
I'm thinking it could be something to do with the ABS module as went into measuring blocks to check the steering, lateral & longitudinal sensors and got error messages (not available).
also when checking CAN Gateway was stating No communication. not sure what this does or if it will have an impact on the 4 wheel drive or even if my car has it.
haldex pump is always showing to be on when engine is running.
have installed a brand new pump & swapped the controller for a supposed working unit. don't want to be changing parts willy nilly if I don't have too.
also when running the output test in ABS I get an error function not available message on the very last part of the test. just after ''EDL/EDS Valves / hydrolic Pump =vbatt, front wheels locked''
hope I'm making sense fell like I'm waffling a bit.