Diff Controller

[20vTurbo]

Currently my S2 has the ABS light on and the diff is locked permanently... regardless of speed. Diff lock button does not work and is not illuminated.

I'm in the process of diagnosis, so any info on what to check and in what order would be great. It's had the gearbox & clutch out recently, together will all the suspension off to swap springs... so I'm thinking it may just be a sensor or alike which has not been put back correctly.

In the mean time, I've disconnected the diff controller so to disengage the diff lock. Are there any ill effects of disconnecting the diff controller and continuing to drive the car?

Cheers

Mick

[UrS4boy]

Rear Differential Lock Controls, the whys/hows for the 92-94 UrS4, 95 UrS6, S2 and RS

I've disconnected the diff controller so to disengage the diff lock. Are there any ill effects of disconnecting the diff controller and continuing to drive the car?

None. Even if the diff lock was working 100%, it disengages at 25 kph. Never try engaging it except at a complete stop.

Here is some reading that might help you sort your issue:

Rear Differential Lock Controls, the whys/hows for the 92-94 UrS4, 95 UrS6, S2 and RS2:

http://forums.quattroworld.com/s4s6/msgs/170940.phtml

Example diagram from that post:

[20vTurbo]

Many thanks... I'll try and interpret that!

Obviously it's easy to feel that its engaged at low speeds, but was afraid that it may still be the case at higher speeds (seeing as there is deffo an issue somewhere)... which I guess would be much harder to feel & confirm.

Is there any case at all in which the diff lock will remain engaged at above 25kph?

[UrS4boy]

Is there any case at all in which the diff lock will remain engaged at above 25kph?

Yes. When the mechanical part (diaphragm inside the activator) fails.

[teejay]

I had that as well.it didnt fail it was just full of dirt and wasnt moving enough to disengage diff lock.cleaning helped and everything's fine now.check if it's moving well with button off/on.

[ericd]

Currently my S2 has the ABS light on and the diff is locked permanently... regardless of speed. Diff lock button does not work and is not illuminated.

I'm in the process of diagnosis, so any info on what to check and in what order would be great. It's had the gearbox & clutch out recently, together will all the suspension off to swap springs... so I'm thinking it may just be a sensor or alike which has not been put back correctly.

In the mean time, I've disconnected the diff controller so to disengage the diff lock. Are there any ill effects of disconnecting the diff controller and continuing to drive the car?

Cheers

Mick

put it all back together and run it with the back seat off and listen for any leaks from the pipes or the t-piece, drive around for a while checking the button , leave it in the
off position (I've seen 1 or 3 that will go off,dunno if this is to do with losing vacuum ?? and it taking a while for it to build up again)

have you visually checked under the rear seat recently ?

[20vTurbo]

Thanks, I'll check, but easier said than done - it's a little difficult to get to and a little noisy in the cabin...

[UrS4boy]

Thanks, I'll check, but easier said than done - it's a little difficult to get to and a little noisy in the cabin...[/IMG]

Put somebody in the car and get it up on a hoist. Have them start the engine and then push the diff lock button while you observe what is happening with the diff lock activator. If it only moves one way, push/pull it back the other way and try again. You will soon figure out what is going on.

[sam80quattro]

if you cut the blue/white wire under the rear seat the auto-unlock wont disengage the diff at any speed either (incase someone has done so) also for experimental purposes I tried locking the diff at speed(80mph+) and it simply slots in as soon as you back off the throttle.. I snapped a rear shaft once and to still use the car (until the weekend when I bought a new shaft) I just removed the shaft but left the cv joint in, started it up and locked the diff, off I went, until it wasn't running right so I tried the old ignition off and back on whilst driving along at 60mph (***** the diff lock switched off)... engaging the diff lock with only 1 wheel turning it is definitely a no no haha it locked but my god what a bang it made

[UrS4boy]

if you cut the blue/white wire under the rear seat the auto-unlock wont disengage the diff at any speed either (incase someone has done so) also for experimental purposes I tried locking the diff at speed(80mph+) and it simply slots in as soon as you back off the throttle.. I snapped a rear shaft once and to still use the car (until the weekend when I bought a new shaft) I just removed the shaft but left the cv joint in, started it up and locked the diff, off I went, until it wasn't running right so I tried the old ignition off and back on whilst driving along at 60mph (***** the diff lock switched off)... engaging the diff lock with only 1 wheel turning it is definitely a no no haha it locked but my god what a bang it made

Seriously not recommended practice.

[20vTurbo]

So in practice, there's little need to use the diff lock unless you're stuck/bogged?

Bearing in mind my S2 is for motorsport use only, and as this generally occurs at above 25kph (hopefully!), I should never need to use it. So would it be sensible to remove the controller and associated wiring/plumbing as part of the overall weight loss program?

Are there any negative ramifications in total removal... warning lights, ECU/ABS issues or codes etc?

[mcandmar]

Pretty much, i have used mine once or twice when stuck in the snow but that's about the extent of its usefulness. You really need to keep that control box on the diff as without it the select lever will flop around. If you want to completely remove it you will have to remove the locking coller and select lever from the diff. You might be able to do so by removing the large seal on that side of the casing, but it would be easier to split the casing and lift the diff out to remove it. To be honest its really not worth the effort as your only talking about two plastic box's that weigh nothing.

[20vTurbo]

OK found the issue, but apparently my description of the problem was inaccurate!

The diff lock was not engaging at all - I think it was the fact that its got track-spec tyres and altered suspension setup which made it feel like the tyres were skipping on lock (like when the diff is locked).

Found that fuse 31 was missing - added fuse and ABS light goes out, and also diff lock engages and disengages on the button as expected.

Doh!!

[SteveH]

It's worth keeping the diff lock to keep you moving, if rather slowly, when you snap a rear driveshaft. I'd save it for that alone, as I can't imagine the wiring of actuator weighs much.

[UrS4boy]

OK found the issue, but apparently my description of the problem was inaccurate! Found that fuse 31 was missing - added fuse and ABS light goes out, and also diff lock engages and disengages on the button as expected. Doh!!

I guess that could have been my first suggestion: Check fuse S31 (but you said the diff lock was always ON not always OFF).

From my Diff lock info post: