VAG Haldex

[Lyons]

Has anyone on here got any means of testing a haldex unit, or know of anyone that can?

 

[svensktoppen]

Depends what you think is wrong with it.

The Haldex control unit itself is basically just a little ECU (a small blue thingy at the back of the car). Then there is the pump for the diff at the rear, the diff itself, etc.

Is it not working properly?

 

[Lyons]

I don't know if its working or not. I just wondered if it could be tested. So it can be replaced independently of the diff? I thought it might all have been 1 unit?

So the haldex, pump and diff can all be replaced individually?

 

[PAULW]

Depends what you think is wrong with it.

The Haldex control unit itself is basically just a little ECU (a small blue thingy at the back of the car). Then there is the pump for the diff at the rear, the diff itself, etc.

Is it not working properly?

Good to hear as I also meant to ask this. I scanned and got this code. Is it the diff itself or code it just be the Ecu?

 

[Jason]

Whats it doing?

 

[PAULW]

Whats it doing?

Brake light switch wasn't working. Replaced it, cleared the code. Took it up the road, saw the traction control light flickering. Scanned it again and that had appeared

 

[svensktoppen]

So the haldex, pump and diff can all be replaced individually?

Yes, they are separate units.

The control unit is a little blue box at the back. It just has electronics, and an ECU with a map for how to shift torque around depending in wheel spin, throttle response, etc. It uses all sorts of sensors on the car, and the ECU, to do this. I doubt it could be diagnosed by anyone other than a specialist, beyond reading error codes via the main car ECU.

The pump is basically just an actuator for the rear diff, and controls the slip. If the pump is broken, the rear wheels will not engage, and basically the car behaves as a fwd car. With an early car without traction control, or with traction control off, it is pretty obvious if this is the case.

A broken control unit would give the same symptoms as a broken pump.

It should be pretty obvious if the diff itself were broken...

Never heard of a broken diff, but the pump can fail. Easy and not very expensive to swap. Mine failed after ~80k miles.

The control unit is easy to swap as well, but not sure if they fail. Never had any issue with mine in 120k miles.

Never heard of the actual diff failing...

Obviously sensors and whatnot can fail.

 

[Jason]

Brake light switch wasn't working. Replaced it, cleared the code. Took it up the road, saw the traction control light flickering. Scanned it again and that had appeared

if that clutch its refering to is the haldex clutch then try changing the oil as it may not be working correctly, after that id say its the haldex pump not operating correctly. The whole things very simple when you work at it

 

[Lyons]

Sven, are the pump or haldex big money second hand do you know?

 

[Graham]

go to a beach and test your diff !

 

[2fast4u]

http://victorborisov.ru/professor/haldex/SSP_414.pdf

Good read to understand the working of the Haldex system. Section on Diagnostics at the end.

 

[Jason]

Sven, are the pump or haldex big money second hand do you know?

haldex units are round 100 and pumps are nothing more than a small remote control car motor in a case, worth around 50 2nd hand.

 

[Lyons]

No way to check if the haldex is goosed then?

 

[Jason]

You can run haldex tests on vagcom to see if it engages or not (ie spin front wheels or not) also you can lay under the car and listen for it engaging but doesnt mean its working.

 

[Gobsheene]

Can the car be taken to a 4 post lift and tried in gear with all 4 wheels off the ground?

Or a rolling road to put some force through the wheels?

 

[Jason]

Won't prove anything

 

[Lyons]

Niall I did that the other day, it proved the diff works to an extent anyway.

 

[Coog]

Can you not take it somewhere slippy and give it the beans?

I can tell what way the transfer case is engaged in the Jeep by flooring it out of a greasy junction.

 

[Lyons]

The prop shaft is out at the minute.

 

[Boydie]

Get a prop shaft and fit it to see if the haldex/diff is working!

 

[Lyons]

That would be the simple solution, but its not that easy Boydo!

I spoke to someone in Skoda yesterday and apparently they have a machine to test the haldex, so I wondered if someone else would to save me buying a prop shaft.

 

[Boydie]

You bought the car orginally though for the quattro/4x4?

 

[svensktoppen]

If it were me I would take it to the main dealer for them to diagnose it. There are lots of things that can go wrong, and all give the same symptoms. Repairs can be done by anyone once you know what the problem is.

And then the usual - make sure the Haldex system is serviced regularly. I just get a service kit from Audi with all the filters and lube, not very expensive. Any garage can do the job, but it is a bit awkward. You need a special wrench for the filter, it is available on eBay for not a lot either. That wrench really makes the whole thing much easier.

Sven, are the pump or haldex big money second hand do you know?

From memory, the pump was not expensive, and that was a brand new unit from Audi. To be honest I would not buy a second hand one, just not worth it as it is likely to fail again. Just get a new one and know it will work for many years to come.

Had a dig through the old paperwork, but no receipt left for the parts. Was back in 2005. Charged ~1 hour work to replace it at an independent garage, after it was diagnosed at Audi.

 

[Lyons]

Cheers Sven.

I hadn't even thought of Skoda diagnosing it, I'd hate to leave it in and them not be able to tell either!

I'll certainly give them a shout though, good call.

 

[Lyons]

Is the rear drive train made up of the diff unit, then a drive shaft on either side? I always imagined the diff was within a solid rear axle unit which went right out to the hub on each side.