Haldex system confusion

A quick update from me, I havent had a chance to do much with the car and have had the dragging problem mainly in the mornings or on a full lock.

I havent taken the fuse out, but had the car up earlier as changed the brake pads and checked the earth strap and it was in fact corroded and hanging off, so replaced this with a brand new one.

I will know tomorrow morning if this has made a difference or not, its quite wet and ive noticed it more so when it is like this, so will update tomorrow and let you guys know if this has made things any better for me at all.
 
Sorry lads my mistake! When i first start the car usually the first thing i do is turn the esp off lol. Yeah i drove off the other day and forgot to turn it off and surely enough the ESP light came on by itself and wouldn't turn off.
I thought you guys meant that the light comes on as soon as the vehicle started, My mistake lol.
Hopefully going to buy another pre-charge pump mid august so I'm hoping that will solve this issue and can put all of this behind me lol.
As ever thanks for all the help!! :D!
 
Just come back from Volks Autos in Sutton. They scanned the car and pulled up faults on both the front wheel speed sensors. They recommended I try changing these and seeing if it cures the problem. Are any of you guys getting any error messages on VCDS?
 
Hey an update from me too, the earth strap for me hasn't made a difference. I also got a sensor error a couple times on front drivers side, don't know if it is this though as its the back that's locking up.
 
The back will lock up as it's the rear diff that's being permanently engaged. The thinking here is that the wheel speed sensors are part of the feedback mechanism to the haldex so if they are knackered then maybe they are causing the issues...
 
Hmmm interesting, I will get the car scanned again and see if the fault is still there and report back.
 
I've asked my mechanic to quote me for this. I think the speed sensors **** up the abs too so might as well change them.
 
the faulty speed sensors are a definite possible reason for the issue. I think I once noted all the reasons down in some old forum posts. Although saying this I haven't actually heard of someone with this same issue and it being resolved by replacing sensors. Most times people don't get an errors of any kind with this problem.
 
Ironically my car has just developed a wheel speed sensor issue on the front right, it's not affected the haldex though, and TBH I doubt it would.

Speed sensor is getting changed this weekend hopefully, for info a new O/S speed sensor was ~£60 from TPS. GSF do a cheaper alternative but I don't trust it!
 
Dave B, the wheel speed sensor (especially either of the front ones) ARE components that feedback to the haldex unit - as ERF quite rightly points out. Furthermore check out the haldex diagram floating around somewhere on these forums that shows all areas the haldex is receiving data and lets not forget the controller itself interpreting it all. This is on the assumption that the haldex unit is doing it's job, but is being fed some dodgy data hence applying the lock at the wrong moment....or the controller itself not interpreting the data correctly. And on the face of it I would have thought this is a real number one cheaper thing to try to do first and replace both front sensors regardless.

Although the possibility is there with the speed sensors I too doubt this is the root cause not because I am an expert, but I base this on what I have read on this subject over the years and following up with others with this issue. So unless someone can step forward and say they had this issue and it turned out to be a faulty sensor then I stand corrected. Solutions varied and have been:
1. replace ABS unit (yes, the ABS unit)
2. rear diff & haldex unit complete replacements.
3. filter and haldex oil change - although many turned out to have short term fixes with this method.

The above is based on no errors from VCDs. Where VCD comms failures occur with the the haldex unix - this turns out to be typically with the classic missing/broken metal strap issue.

Question again, has anyone actually had the same issue with no VCD errors and the fault turned out to be the metal strap ?

One of my biggest concerns is when 'many' go for option 2 and find they still have a problem all because they are not totally sure of the donor parts with this problem being so widespread. Case in point if I have a light front end collition and the car is written off (which I would ask for !) who will be buying my so-called low mileage parts ? Basically bit risky and be very wary, but has turned out well for most !
 
Can anyone shed any more light on this plug?? He seems to be the only person to cure this problem??
many thanks!
 
I've changed my earth strap, checked the plug at the rear of the diff, it was fine, I even checked the pump plug and that was fine. If I remove the fuse the wheel dragging stops, but obviously it's only working in fwd...
So the list of faulty components could be;
Haldex clutch plates
haldex controller
wiring loom and connectors
haldex pump
precharge pump?
anymore?
Theres a post on page with someone saying they had a faulty connection on a "plenium" sorry if I'm being stupid but I've no idea what he means?
Cmon lads let's put this fault to rest!
 
Big Bang Yam, replace the whole rear haldex as many do and your effectively replacing everything in your list. Sadly - for us - that's what many do (and lucky to get good replacements) than faff around each part.

I know of a guy, who went through the whole process with Audi Dealership and replaced the whole rear end only to find it was the abs unit...(although a bit on the rare side - it's still possible). very costly !
Oh and if it's a list you want add the front left/right sensors too.
 
Yea I know , there's so many variables to go wrong, not really enjoying the car either which don't help. Still would like to know what member posted about poor connection.I've looked on loads of forums and everyone is chasing their tails trying fix it , complete nightmare I'd say!!
 
superkarl said:
what faults are you getting in vagcom?
Click to expand...

This is one of the biggest issues - if only there were any. As I said most do not report any errors.
most probably a transient error not picked up by vagcom or something not computer controlled - I guess.
 
wheels locking is diff. it has to be surely. the haldex doesnt regulate left-right, its front to rear. the diff does the left to right bit. so 'scrubbing' whilst turning must be the diff. hence no errors, the diff isnt electronic
 
superkarl said:
wheels locking is diff. it has to be surely. the haldex doesnt regulate left-right, its front to rear. the diff does the left to right bit. so 'scrubbing' whilst turning must be the diff. hence no errors, the diff isnt electronic
Click to expand...

Not quite...if it was purely the mechanical, pulling fuse 31 wouldn't solve the problem, but it does (in my case at least!). Having my speed sensors changed next Friday, by which point I have chnaged everything (inc. the rear diff), except for the pre charge pump...
 
I'd say the haldex unit is stuck in awd and not allowing the outside wheel to rotate faster then the Inside.so what ever controls the haldex must be faulty, is there a pressure regulator valve or something that's not releasing the Pressure of the haldex clutch? Does anyone understand how the controller works?
 
Erf the pump must be working or the car wouldn't be stuck in awd, when the fuse is removed there is no longer power to pumps?
 
I hope these are of use ;)

Regards
Rick

How it works http://rickpiper.cbfsim.org/files/haldex.pdf

haldexservicing_small.jpg
 
Big Bang Yam said:
I'd say the haldex unit is stuck in awd and not allowing the outside wheel to rotate faster then the Inside.so what ever controls the haldex must be faulty, is there a pressure regulator valve or something that's not releasing the Pressure of the haldex clutch? Does anyone understand how the controller works?
Click to expand...
the haldex doesnt regulate drive left-right, its front-rear, as its on the end of the prob BEFORE the diff.
the precharge pump regulates the pressure to the plates, through a valve inside the haldex controller

perhaps with the awd on the scrubbing is only felt due to drive to the rear wheels, when in fwd the wheels are just coasting so maybe not as noticeable
 
*edit
but surely when the fuse is removed if it were a faulty diff it would still drag a tyre? But as stated when u take the power away from the haldex the wheel dragging stops,
 
Last edited:
I'm new to this thread but I have the same rear diff locking issue when maneuvering at low speeds.

TTs CSCC DM

The only difference is that ours is an Audi TT race car with a race Haldex Controller.

At first we thought it was the race controller that was causing the issue, but when we replaced it with the OEM controller it was almost the same (just a little less).

The strange thing is that putting the handbrake on one click should disengage the Haldex controller altogether but on our car it makes no difference. Disconnecting the Haldex by unplugging it works though.

Here's what we have done so far:

1) Changed the Haldex and Diff oil and filters
2) Changed the Haldex unit (x3)
3) Change the entire rear diff (Diff, Haldex, Pump etc.)
4) Test all of the sensors (Wheel Speed, Steering Angle, Accelerometers etc in VagCom)
5) Test the Haldex pump using vagcom
6) Strip the original diff down and totally clean it, check it and re-assemble it.
7) Replace the Earth Strap.

Conclusions:

1) It's not mechanical (tried two total new rear diffs and stripped one down just in case).
2) Its not the pre-charge pump (tried two and also striped one down to double check, plus did the pump test on VagCom)
3) It's not the Haldex unit (we have tried three now)

So What's left?

Two key facts:

1) Handbrake test (doesn't make any difference)
2) Unplugging the Haldex frees it all up.

Therefore I can only conclude that it is something electrical, I'm back at the workshop tomorrow and I am going to go through the whole circuit diagram and vagcom test on the ramp to see if we can nail this down - it's a matter of honor now!
 
FreeRideSkier said:
I'm new to this thread but I have the same rear diff locking issue when maneuvering at low speeds.

View attachment 5864

The only difference is that ours is an Audi TT race car with a race Haldex Controller.

At first we thought it was the race controller that was causing the issue, but when we replaced it with the OEM controller it was almost the same (just a little less).

The strange thing is that putting the handbrake on one click should disengage the Haldex controller altogether but on our car it makes no difference. Disconnecting the Haldex by unplugging it works though.

Here's what we have done so far:

1) Changed the Haldex and Diff oil and filters
2) Changed the Haldex unit (x3)
3) Change the entire rear diff (Diff, Haldex, Pump etc.)
4) Test all of the sensors (Wheel Speed, Steering Angle, Accelerometers etc in VagCom)
5) Test the Haldex pump using vagcom
6) Strip the original diff down and totally clean it, check it and re-assemble it.
7) Replace the Earth Strap.

Conclusions:

1) It's not mechanical (tried two total new rear diffs and stripped one down just in case).
2) Its not the pre-charge pump (tried two and also striped one down to double check, plus did the pump test on VagCom)
3) It's not the Haldex unit (we have tried three now)

So What's left?

Two key facts:

1) Handbrake test (doesn't make any difference)
2) Unplugging the Haldex frees it all up.

Therefore I can only conclude that it is something electrical, I'm back at the workshop tomorrow and I am going to go through the whole circuit diagram and vagcom test on the ramp to see if we can nail this down - it's a matter of honor now!
Click to expand...

The only time I've heard this kind of story is when it turned out to be the ABS unit - another expensive replacement at about 1K
 
What functions does the abs unit do to influence the rear diff though??well done freeride !! Get yourself involved!
 
thegoal007 said:
The only time I've heard this kind of story is when it turned out to be the ABS unit - another expensive replacement at about 1K
Click to expand...

It could be the ABS unit but the issue that makes me doubt this is that the handbrake on one click doesn't disengage the diff. The handbrake signal goes directly to the Haldex unit not via the ECU or ABS units. So it looks like the Haldex isn't getting the signal (although VagCom finds the Haldex unit on the CAN bus).

Here's the Haldex Manual for anyone who hasn't seen it yet: http://www.billswebspace.com/HALDEX.pdf
 
mine seems to be cured,,,changed the haldex oil and filter and its driving lovely...completly different car!!!i know its been said but it could possibly be the cltches dragging???or,,,,,i remember reading that the haldex takes more fluid then what is in 1 of those cartridges..now i wonder if the dragging problem is by factor of not enough fluid...or the pressure sensor is closing moving the clutch plates to protect them from damage due to lack of oil? and the sign is the dragging wheel? to properly check the oil level on that haldex is nigh on impossible due to the location of the of the level plug!!
 
Big Bang Yam said:
mine seems to be cured,,,changed the haldex oil and filter and its driving lovely...completly different car!!!i know its been said but it could possibly be the cltches dragging???or,,,,,i remember reading that the haldex takes more fluid then what is in 1 of those cartridges..now i wonder if the dragging problem is by factor of not enough fluid...or the pressure sensor is closing moving the clutch plates to protect them from damage due to lack of oil? and the sign is the dragging wheel? to properly check the oil level on that haldex is nigh on impossible due to the location of the of the level plug!!
Click to expand...

erm, re-read my post #131 above.....basically one of the possible fixes and this maybe short time, but hopefully your one of the lucky ones if you are not sure of the history of changes of your haldex fluids.
 
FreeRideSkier said:
It could be the ABS unit but the issue that makes me doubt this is that the handbrake on one click doesn't disengage the diff. The handbrake signal goes directly to the Haldex unit not via the ECU or ABS units. So it looks like the Haldex isn't getting the signal (although VagCom finds the Haldex unit on the CAN bus).

Here's the Haldex Manual for anyone who hasn't seen it yet: http://www.billswebspace.com/HALDEX.pdf
Click to expand...
oh, I wasn't aware of that. I do know the handbrake trick didn't work for them also, but it is still turned out to be the abs. Maybe there was a combination of issues where he was concerned - I can't explain that. All I know was it was the same story and that is how it was fixed albeit via Audi Dealers.....so, the skeptic in me says you can never know or trust what they really done.
 
thegoal007 said:
oh, I wasn't aware of that. I do know the handbrake trick didn't work for them also, but it is still turned out to be the abs. Maybe there was a combination of issues where he was concerned - I can't explain that. All I know was it was the same story and that is how it was fixed albeit via Audi Dealers.....so, the skeptic in me says you can never know or trust what they really done.
Click to expand...

Maybe worth a try as we have changed everything else. I recently tested the signals on the Haldex connector to check that the handbrake and foot break signals were getting through, which they were.

In the Haldex manual it stated that the handbrake and foot break direct signals override everything and switch off the rear diff. Clearly this is not the case as we have tried 3 x Haldex Controllers, 2 x Complete rear Diff. and checked all of the wiring and sensors (wheels sensors x 4, Accelerometers etc.).

We took our TT race car out on track last week at Mallory Park and the race Haldex was definitely working at full speed, you could really feel it stabilize the rear under breaking (only available in the race Haldex version).

CSCC TT LR

So it's just the low speed locking that's the problem?
 
Essentially, if all sensor inputs and PLU programming results in the sole activation of the valve in the Haldex unit via the stepper motor, then some way of showing/logging what signals are being sent to the motor would be the ultimate diagnosis tool.

I don't know how possible this is i.e. whether there is a signal wire in the Haldex connector or a logging code for this signal which VAGCOM can read or even if you can open it up and splice a signal wire in for monitoring (I saw a recent disassembly of a Haldex controller on here) ?

The it would be a question of mapping the actuation of the motor with the operating conditions of the vehicle to give a better picture. For me though if the VAGCOM logging shows no issues with sensors or actuators in the Haldex and other systems then electrically the system 'should' be working as designed and so there must be an obscure fault - which is perhaps why they are so difficult to diagnose.

My other thought is that if the stepper motor has somehow lost it's calibrating point or is not calibrating then Haldex may be operating electrically correctly but having an incorrect mechanical effect.

Disconnecting the prop-shaft may also have some diagnostic benefit because it would also eliminate a critical element of the system i.e. if the rear still drags it must be a mechanical fault.

Martin
 
Last edited:
k1ano said:
Disconnecting the prop-shaft may also have some diagnostic benefit because it would also eliminate a critical element of the system i.e. if the rear still drags it must be a mechanical fault.
Click to expand...

No need to disconnect the prop shaft as unplugging the Haldex unit or removing the fuse has the same effect. If it's still dragging it's a mechanical issue. But in most of the cases above the rear diff seems to be ok.
 
Sorry been away for a bit lads, i'm taking my car down to mrc next week so i'm going to ask them what they think it could be and i'll post back here and let you all know their input. Has anyone tested the replacement of the speed sensors? Has this helped??
I havent seen this error pop up on vagcom but i will plug it in tomorrow and see what i find.
Thanks lads!
 
audi upgrades
I havent had any more sensor errors on my car since I reported them a while ago, I did change the brake pads, so not sure if it was just loose or something, but it hasnt been back since.

I am still getting the dragging issue though, more noticable when its wet, Ive noticed it seems to be even worse when going in reverse as well and im also getting the traction light come on when taking corners but only slightly.
 
I can say that when my S3 did this it turned out to be corroded ABS wiring on the front drivers side. Caused no end of issues but all thankfully resolved with a few meters of wiring and some solder!
 
Hi all - newbie here!

Picked up a 1.8t quattro 8L and it's suffering from the same symptoms mentioned in this thread. Thanks to the above info though I've just run outside and removed fuse 31... and the low speed locking up is gone! :)))

BUT as it's a horrible cold wet night with lots of leaves about i decided to 'test' what happens without the fuse at although it's 'fun' as it feels like there's no traction control the rear wheels are still joining in. A gentle launch on loose gravel (enough that would make the wheels of a FWD car spin) I still felt a judder from the rear. So I'm confused!
 
audi upgrades
juddering on wheel spin - that sounds about right to me if the haldex fuse is out.

Also my abs doesn't work with the haldex fuse out.
So basically you're at the same point as everyone else with this problem. remove fuse - issue gone.
 
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