Is my AWD working?

[samiam]

Yeti 2014 tdi 4x4 DSG
I was towing a trailer today and drove onto some wet grass, the front wheels spun immediately and there was no sign of any action from the rears. Putting it in ‘off road’ mode made no difference.
I’ve been suspicious of the drive for a while as something hasn’t seemed as I might expect. It’s felt like a fwd, not an awd.
What can I do to confirm or deny that the AWD is functioning? How do I troubleshoot the drive components and/or controls?
Any known issues?


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[Scott K]

If you can get it scanned, any Haldex fault should be logged. The offroad mode only engages extra electronics - it doesn't engage the 4 wheel drive.
Have you had the Haldex oil changed? I have seen reports of failure due to low battery level but not sure on that.
When the wheel slipped did you accelerate or ease off? In my car, if you accelerate this engages the haldex but if you ease up or brake, the slipping stops and the car doesn't engage the rear.

[samiam]

I haven't had it scanned, I'm just coming up to 60K, so the fluids are due for their first change around now and a scan while i'm at it. I tried both accelerating and backing off to get anything to happen, nothing did. I have little faith in the dealers, they seem to be able to perform only the most basic scans and show absolutely no ability to genuinely troubleshoot anything beyond the most basic.

[samiam]

It turns out the pre-charge pump on the Haldex is showing a fault.
Are they repairable, or more to the point, is it wise to repair?
What about replacement options?


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[Crasher]

Pre charge pump failure is common and the pump is replaceable, part number 0CQ 598 549 at £234.24 inc VAT retail. Unfortunately I have known people get caught out with this and find out it is the control unit that has failed, not the pump. These are part number 0AY 907 554 J and costs £373.74.

One fault this unit does suffer from that causes drive failure is the input shaft snapping and this does not show up as a code, this failure means you need 0CQ 525 554 D Four-wheel coupling £1784.02...

[samiam]

Ok, let’s drill down into this a bit then. It looks like the re-charge pump is relatively easy to remove. If I take it out I assume I can test it to ascertain if it’s kaput. Does it tend to be a pump failure or the electric motor that drives the pump that craps out.
This 2014 car has only done 60k.
If it’s the pump, what would cause such a low mileage pump to stop pumping? Blockage? O-rings?
So would I be right to primarily suspect the motor? Does it get water (or fluid) into it and corrode/burn out? Or does it tend to have a weak link in its wiring that causes a broken curcuit?
I presume taking the pump out drops all the fluid out of the Haldex? Or does it only loose a little? I will, of course fully change the oil once I’ve fixed the fault, but I’d rather not prior to getting it all sorted.

[Crasher]

Yes it is a circa 12v pump but it’s free load spin speed is no indication of its ability to provide pressure by which you can make a judgement of using a diagnostic system in output tests and watching the results in measuring blocks to see if the pump can deliver pressure. The trouble is it may fail to satisfy the specs due to the ECU being unable to provide it with sufficient current. It could also be an internal fault within the Haldex which is not unknown, for these reasons (I.e. covering ones ****) we “encourage” people to have the full unit which deals with most eventualities and has a 2 year VAG warranty which is comforting.

[samiam]

The thing is I have zero faith in the dealer. They just throw expensive parts at a problem and, if that doesn’t fix it, throw more expensive parts at it.
So what I’m trying to do here is to KNOW what’s wrong.
I’m still struggling to know how to eliminate everything else.

[Rob69]

I thought a Haldex oil and filter change was a lot sooner than 60k, more like 20 or 40?

[stuart]

My 2014 Skoda Superb was in the dealers for it's service last June, so 2 years old and it was due on the service schedule as 2 years, not sure on the mileage think it is 40000 miles but as mine only does 6-7000 per year it was a time based thing, due again June 2019

[Crasher]

I’m still struggling to know how to eliminate everything else.

You can’t. You have to make educated guesses based on the tools, experience and time to hand. The £200 ish for a new pump is a cost effective way to see if the ECU is faulty as if it is, the incorrect part you have replaced is the cheapest and barely the cost of two hours main dealer diagnostics.