S2 ABY Diff Lock Actuator and Switch

[hashluck]

Just spent an interesting afternoon fault finding my intermittent Diff Lock - have established that when the system works it works but sometimes the Diff Lock switch on the Diff does not send the signal to the ABS controller to switch the ABS Off and light the green LED on the Diff Lock control switch in the car.

Both the actuator and the diff lock switch are not original items. The actuator is very lazy and slow and the lever arm quite rusty and it is the Mercedes item we often see fitted. The switch I am not sure of where it is from but it has a different connector the the original.

I would like if possible to fit an original actuator and switch - can anyone help me with part numbers and availability of both?

Thanks in advance

[Tractor Dave]

If its working intermittently and or slowly its more likely a vac leak somewhere in the pipes. Disconnect the two pipes to the actuator and try sucking each tube alternatively. You should see movement of the arm. The Mercedes unit is identical to the Audi one but only has two mounting holes. Its even made by vdo. I do have a switch here somewhere if you want to try that and also a good used late avant actuator with the connector plug. Tradition were selling the actuators for very silly money but they seem to have sold out.

[hashluck]

Ah thanks Dave. I had incorrectly assumed that if the actuator was moving albeit slowly that the vacuum was OK. I will remove the rear seat and check as you suggest and if anything obvious amiss. I would like to fit the correct switch so I will message you on that, Actuator. will depend on the vac line tests I guess,

[hashluck]

If its working intermittently and or slowly its more likely a vac leak somewhere in the pipes. Disconnect the two pipes to the actuator and try sucking each tube alternatively. You should see movement of the arm. The Mercedes unit is identical to the Audi one but only has two mounting holes. Its even made by vdo. I do have a switch here somewhere if you want to try that and also a good used late avant actuator with the connector plug. Tradition were selling the actuators for very silly money but they seem to have sold out.

So the blue pipe is not holding vacuum and I assume it should? No obvious leak in the rear seat pan area will get back under the car, Yellow pipe holds vacuum and moves the actuator.

[hashluck]

Further update - the blue pipe tested in isolation holds vacuum. Plug it into the actuator and it does not hold and applying vacuum does not move the lever. This would suggest the actuator at fault?

[newsh]

Further update - the blue pipe tested in isolation holds vacuum. Plug it into the actuator and it does not hold and applying vacuum does not move the lever. This would suggest the actuator at fault?

Yes it sounds like the little diaphragm in the actuator is split.

[Crasher]

Part number 8A0 711 995

[hashluck]

Thanks. I did find the correct replacement and fitted it and all has been fine since.

[hashluck]

Hmm my Diff Lock has failed again completely - same symptoms as above, the Diff Lock switch yellow triangle lights up (AND the Diff Actuator arm moves) BUT no green LED light on the switch display and no ABS light on dash.

The diff actuator is virtually brand new so would be surprising and disappointing if that so I am now thinking the Switch which from memory is not OEM. Can anyone please provide a part number for the correct switch? Thank you

[JayCab]

That page should help

[JayCab]

https://www.autewo.de/893919167-audi...erentialsperre

The part looks unobtainable now.

I do not have an S2, but I am an electrical whizz good with fabrication. If you actually have a broken switch, the pinout of the DIFF switch looks the same as the fog light and general dash switches. My money says you could buy a fog light switch, swap the front plate with "DIFF" written on it, and have an effectively new OE part...

You can get these switches much more easily, but hold onto that "DIFF" frontplate for dear life

[JayCab]

Problem could also be with something on part # 893919216, which looks like a daughterboard next to the main switch in the same housing.

893919216 is also unobtainable, but it's the sort of part that probably has a power distribution relay on it. It probably takes the single pole on/off from the DIFF switch and sends that onto other modules, such as ABS, cluster, ECU, whatever else needs to know the difflock is engaged.

My next money would go on inspecting that PCB for dry joints and re-flowing, bearing in mind it's also a rare part.

[hashluck]

Ah sorry I did not explain myself at all well. I meant the elecro-mechanical switch on the diff itself, nothing to do with the centre console switch

[hashluck]

For those who find this thread, this is a great resource https://www.audiworld.com/forums/aud...-urs6-2822954/

The Switch Part No, is 013941521a but seems unavailable. There are some reverse light switches and similar out there which claim to be compatible but I have my doubts. Looking for anyone's real world experience of a compatible switch or a good used part.

[sal_s2]

Does the avant have the same part? If so I should have a spare