Diff lock still engaging by its self, help

[220bhp]

My difflock keeps locking itself,which is quite dangerous. I have to fix this as its coming up for an MOT, and the ABS light is on on the dash which will be a failure.
up untill now I have pushed the leaver on the diff and the lock has been deactivated,but the abs light and the green light on the switch stays on.
But now I cannot move the leaver at all, it seems to be stuck on permently,so I can't even cable tie it. the odd thing is it has never worked in eight years of ownership,press the switch and nothing happens.So why it has started to turn its self on is a mystery.
I need to disable this asap including the abs light,so any help or advise would be much appreciated.

[UrS4boy]

My difflock keeps locking itself,which is quite dangerous. .....So why it has started to turn its self on is a mystery..

Normally the lockable rear diff is activated via a diff controller and a vacuum switch. There is a check valve in the system (to prevent boost from reaching the diff lock actuator) that most likely has failed. Yours is coming on under boost and there is no vacuum to pull it off again. You need to replace the 046905291A check (aka "non-return") valve. See below:

Detailed diff lock info: http://forums.quattroworld.com/s4s6/msgs/170940.phtml

[murat]

I had a similar issue. my difflck was engaging manually. the reason was the vacuum hose was disconnected in some place. you can check for a hose split or disconnect.

[ash2050]

I had the same problem on mine.

The ABS light and Diff lock indicator light used to keep coming on under boost.

I replaced the valve which was £14 from stealers and its sorted the problem out.

Simple and cheap fix :-)

[chezz]

[QUOTE=220bhp;699541]My difflock keeps locking itself,which is quite dangerous./QUOTE]

Never a truer statement..Some people are trying to induce this situation - insanity? Dangerous? and their insurance will certainly be void...tyres destroyed in a very short space of time...but that's another story altogether.

[ericd]

I'm sticking this in an old thread as current situation is same as OP

On a 3b

Switch on ignition, diff green led is lit (engine running or not), abs light on dash is lit, "diff" button not depressed (no orange triangle), however when "diff" button depressed (orange triangle lit), the diff control unit under seat can be heard clicking on/off etc

Green led constantly on and diff is engaged constantly, crabbing and scrubbing at slow speeds when turning etc, i've worked my way through various threads about check valve failure and just looking for opinions , and also is there another way of disabling/unlocking a locked diff while waiting for another one way valve ???

[sam80quattro]

Jack it up, remove the pin on the actuator/diff lock arm and push the arm, cable tie it to stop it moving

[ericd]

I'm sticking this in an old thread as current situation is same as OP

On a 3b

Switch on ignition, diff green led is lit (engine running or not), abs light on dash is lit, "diff" button not depressed (no orange triangle), however when "diff" button depressed (orange triangle lit), the diff control unit under seat can be heard clicking on/off etc

Green led constantly on and diff is engaged constantly, crabbing and scrubbing at slow speeds when turning etc, i've worked my way through various threads about check valve failure and just looking for opinions , and also is there another way of disabling/unlocking a locked diff while waiting for another one way valve ???

update: got a new one way valve (as previously mentioned in this and other threads) and after a wee run and some button pressing my diff is now unlocked

[newsh]

Nice cheap fix!

[UrS4boy]

Rear Differential Lock 101

update: got a new one way valve (as previously mentioned in this and other threads) and after a wee run and some button pressing my diff is now unlocked

To remind others, when that one-way check valve fails on the differential lock system, it allows boost pressure from the intake manifold past the valve and into the differential lock activator, i.e. everytime you get into the boost, the push/pull diff lock mechanism would be activated, engaging the diff lock. Furthermore, with no or limited vacuum to pull the diff lock off, it might remain on, as experienced.

Rear Differential Lock 101:

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