# Haldex not working... and I'm about to turn crazy



## 2west (Nov 9, 2011)

Hi guys,

I live in Canada and winter is about to begin. I bought an Audi TT 2001 180hp Quattro manuel 5 spds few weeks ago. I did quite a lot of work on it since to put it back straight. I was thinking the AWD was working at first but my lack of knowledge doesn't allow me to detect the not working AWD... It was the first time I drive a TT. So I bought it that way.

I'm new on the forum but not new at mechanics and cars. To tell the truth I'm a technician in a VW dealer.

Here is the problem, there is no way to make my AWD Haldex working. I replaced my Haldex controller tonight expecting to solve the problem but no cigar. I red a lot on many forums before posting here.

There is only 2 things that remain uncheck on my car. The precharge pump and the rear diff clutches... And I don't feel like changing the rear diff... though I don't think it's the problem. I think the rear wheels should try to turn with the 4 wheels in the air at least a little bit with worn clutches, but the don't turn at all...

Here is what have been done yet:

-Replaced longitudinal accelerator sensor G251
-Check 5Amp fuse and it's good
-All wires at rear connector checked
-central drive shaft is turning
-enough oil on the haldex
-replaced the haldex controller
-No brake system faults
-No engine faults
-No MIL lights on the dashboard, ESP and ABS work well
-Ground strap on the rear housing present and working

Ask if I forgot some, but I've checked about anything... Your experiences could really help me out here!

What about the precharge pump. How it's involved in the whole mechanism... I used to think it was just to lock the rear differential.

thanks all!


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## techfreak (Aug 13, 2010)

I think you've pretty much covered everything, use googlesite search on this forum to search for haldex issues and info on the pre charge pump should come up.

You've changed/checked everything else, I would be doing the pre charge pump next before looking at diffs, unless of course you can diagnose it as 100% the diff 1st

Oh and as an after thought, was it a new haldex controller? Or a 2nd hand? Could be a dead one itself?


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## 2west (Nov 9, 2011)

Just to make a follow up...

yes it's a second hand... even at my price a new one was 1150$ CAN... I tought it was damn expensive... So I found a 2nd hand one for 200$... Therefore I can communicate well with everything and make the test work.

Today after work, I asked to a coworker friend to sit on the passenger seat with the VAS. After few test drive, we finally saw the trouble code 01155... that is clutch mechanical failure... but the code was written as intermitent. After few search on the web, I found that code to happen to be sometime linke to the pricharge pump that doesn't make his job... next job for me.

So I'm gonna see if that pump is working and change it if needed... I'm gonna keep posted... Anyone already had the code 01155?


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## FinTTq (Sep 23, 2010)

Common symptoms for a haldex pump failure. Just replace it and it will be sorted.


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## Mondo (Feb 20, 2009)

Happy problem hunting. Can't help, other than to say you're right; all 4 wheels should spin slowly if she's off the ground and in gear, idling. I know as that's how mine behaved when I got my performanced Haldex fitted. Kinda weird seeing all 4 wheels going around with her off the ground. Weird, but nice to know I do actually have 4WD.

As you will too shortly, I hope.


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## 2west (Nov 9, 2011)

There is a R32 that came at the garage today... a model that is quite rare in Canada. we've been able to make the test... And yes, absolutly no time or hesitation or need to give throttle. As soon as you release the clutch, all 4 wheels begin to turn!

A new pre charge pump is 500$ at my price lol... lucky I know it's available on the second hand market...

I also found a 2 pins male connector today. I'm gonna be able to see if there is voltage that comes out of the controller to activate the pump at startup and after that I'm gonna see if i hear the pump working with my stetoscope if I put voltage on direct at the pump, I know it supposed to be quiet.

Probably ending changing it anyways as after that I'm gonna have to change the whole unit or to rebuild it.

Thanks for all your inputs, I'll keep you aware!


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## rideone (Nov 13, 2012)

I am having the same problem with intermitant awd. i checked all connectors . vag getting 01155 i disconnected the precharge pump and put 12 v to it. it sounds sick... gather this is my next step to replace it. anyone go through this and had good luck by just changing it ? :?:


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## TT-TOM (Feb 15, 2012)

I'm not sure if I'm right but when I was flashing my ECU I heard a noise from the back of my car and it could only have been the haldex pump running so they aren't silent. You would never hear it with the engine running though


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## gunner (May 18, 2002)

Ive had exactly the same problem with my haldex and have been searching for a solution before attempting to change anything.

There's an interesting thread Here which discusses various theories and solutions. One guy suggests using Vagcom to run diagnostics on the pump, cycling it on and off, which subsequently appears to solve the problem until the next cold start in the morning.

From what I gather the problem can be caused by one of several factors including a) blocked breather hole, b) lack of oil, c) haldex pump not working, d) rear diff earth strap broken, e) bad connectors and f) faulty ABS unit.

It seems to be a mysterious problem and I wish someone could come up with a definitive answer.

By the way, you can buy new haldex pumps on eBay UK for £140 + pp, the seller also claims they can recondition old pumps, presumably for less, see Here


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## EscapeOfficer1 (Jul 19, 2010)

Hi Zwest...Here's a trail of technical communications that Wak had with Haldex in Plymouth MI USA.

http://www.wak-tt.com/haldex/haldexfuse.htm

If the info within is of any help all good, if not you could contact Haldex in the US - a bit nearer for you in Canada..?

Also, was the 5a fuse no 31..?

Next time I'm under mine I'm going to check the earth strap as I've seen alot on here about it.

EO


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## 2west (Nov 9, 2011)

Hi to everyone folks!

just realised how long I started this post and decided to come see how it gets and to give you feed back.

After many other tests and lots of research, I think I'm almost a first generation haldex system expert now!  About my problem, it was the pre charge pump that was defect. There's been an oil leak from the seal that eventually fill up the motor case, spills inside the motor itself, causing an abrasive paste that eats commutator and brushes. Result: no power on the motor, no pressure build up, no system priming. I was able to make it works with 12V directly on it but didn't las tlonger than one drive cycle.

I worked on it since and to tell the truth, I'm in my way to make an aftermarket billet precharge pump that won't fail for a better price than the one from the dealer. But I still need some time to make it right. By the time also, I'm developping a replacement motor for those who would just like to rebuild their own pump. Most of the time, the pump is good and the motor is the trouble. The motor gonna have my own specs and will bolt right back at the place of the other... Almost the same as the one sold for 140 pounds on ebay but for less money.

I'm impatient to show these to you guys. If some of you have problem with their systems, feel free to ask, I'm sure I'm gonna be able to give good tips!


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## rideone (Nov 13, 2012)

Thx for the replies. 2west where e you? I amh toronto area. How long before y
ou have a prototype? Do


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## 2west (Nov 9, 2011)

rideone said:


> Thx for the replies. 2west where e you? I amh toronto area. How long before y
> ou have a prototype? Do


I'm in the Quebec city area. For the billet assembly, I expect 12 to 15 weeks before I finalise to test the first prototype. Therefore, I should have the electric motor itself finalised to be tested in a couple of weeks. Worst case I'm gonna be able to rebuild original pump at this time.


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## rideone (Nov 13, 2012)

2west i have found a used one that will hopefully get me through this winter though would like to know how you make out and have you possibly look at my old one to see if you can recondition or replace the motor in it so i have a spare for when the second one fails. I will be getting this used one next week and will let everyone know after complete how i made out. Anyone in toronto ontario area that has a haldex filter tool they could loan me please let me know. thx


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## 2west (Nov 9, 2011)

rideone said:


> 2west i have found a used one that will hopefully get me through this winter though would like to know how you make out and have you possibly look at my old one to see if you can recondition or replace the motor in it so i have a spare for when the second one fails. I will be getting this used one next week and will let everyone know after complete how i made out. Anyone in toronto ontario area that has a haldex filter tool they could loan me please let me know. thx


I can recondition it no problem. I'm pretty confident with the new motor I will get but I want to be sure before. I'm gonna get back to you with the developpement.

Besides the AWD no working properly, theses pumps when they fail (and they will all fail eventually because of the way they are made) can cause more problems. One problem is the way the motor behave when failling it's not like ON/OFF working or not working. His gonna slowly decrease his torq and begin to produce less pressure in the system. Besause there is also a mechanical pump into the differential, when the system is primed properly even with a pump that is not in top shape, the system won't wear. Therefore, at a point where the pump is still working but not enough to prime the system correcly it can result in clutch slippage and premature wearing on them for an end result of bad clutchs and no more AWD. When it happens the differential have to be taken out and clutch replaced.


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## horror (Feb 18, 2011)

Does a simple tweak exist to electrically/electronically fool the haldex system to lock either the central differential, the back axle or both.


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## 2west (Nov 9, 2011)

horror said:


> Does a simple tweak exist to electrically/electronically fool the haldex system to lock either the central differential, the back axle or both.


you have to know there's no central differential on a Haldex system. There's a propeller shaft that goes from the front transmission/differental of the car that is always sendind power to the rear. Your Haldex system is at the rear just before the rear differential. (Basically they are a single unit). When the Haldex become in fonction, it just transmit the power into the differential to the rear wheels.

To answer to your question. There's no easy way really, and beware on some modifications that are written trough internet, some of them are false and will just make you damage your system.

What you need to acheive what you want is a Haldex controller... refered as blue or orange controller or race controller. I saw also a in dash dial controller also that was used in a rear swap from a TT to a MKIV.

Do your search but some of them will have behaviours different depending on what you want. The performance Haldex one keep the safety carateristics that is very important from my point of view. If your goal is only track specific, you can make what you want.

Basically these controller just change the control valve setting and opening that is integrated into the controller. That could give you no slip start. It increase torque at lower speed and from lauch or things like 50/50 always on. Some company manage to control only that valve from open to close position with intermediate positions. It won't module depending on the data inputs from the other ecu like lateral or longitudinal Gs, throttle position sensor, brake on/off etc...

So another way to answer at: Does a simple tweak exist to electrically/electronically fool the haldex system to lock either the central differential, the back axle or both? Is to say yes, if investing 550-1050$ is an easy tweak for you!


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## horror (Feb 18, 2011)

Thanks for your reply.
My goal was to achieve 2 or 3 driven wheels to get out of a muddy field or track, i.e [almost] AWD.


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## 2west (Nov 9, 2011)

horror said:


> Thanks for your reply.
> My goal was to achieve 2 or 3 driven wheels to get out of a muddy field or track, i.e [almost] AWD.


Your system in a stock configuration when working properly will acheive that easily. In fact, a properly working system will begin to transfert power at the rear wheel as soon one wheel at the front spin for 15 degree. That means the rear wheel will start to track probably before you even notice the front is spinning. From that moment when one or both front wheel spin there is pratically no delay for the back to be in fonction because the system is primed from the start via the precharge pump.

With the EDL it offers a kind of front wheel torque repartition if slippery in the front but not on the rear.


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## 2west (Nov 9, 2011)

rideone said:


> 2west i have found a used one that will hopefully get me through this winter though would like to know how you make out and have you possibly look at my old one to see if you can recondition or replace the motor in it so i have a spare for when the second one fails. I will be getting this used one next week and will let everyone know after complete how i made out. Anyone in toronto ontario area that has a haldex filter tool they could loan me please let me know. thx


I've almost finalized the test of the new motor! I'm very happy with it, works real great. I have still few things to control but I can state it as a sucess! :mrgreen:


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## RussAdams (Feb 21, 2017)

2west said:


> I've almost finalized the test of the new motor! I'm very happy with it, works real great. I have still few things to control but I can state it as a sucess! :mrgreen:


Hi 2west,

Did you ever complete your project and have motors available for rebuilding a TT's haldex?

Russ


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## fire88 (Jul 15, 2021)

Hi mate

It's nearly 10 years ago. 

Sent from my GM1900 using Tapatalk


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## RussAdams (Feb 21, 2017)

Hope springs eternal!

Best thread I've been able to find on rebuilding a Mk1 haldex.

These cars are getting rarer and parts harder to find.

Grasping at threads I suppose.


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