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Old 07-09-21, 05:04 PM   #1
BackintheFold
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Default J187 relay for diff lock. MB quattro

J187
Can’t edit title! Can anyone tell me where this relay is located please? A photo would be perfect.
Thanks!
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Last edited by Isimmo; 07-09-21 at 10:00 PM. Reason: Wrong relay number [title edited by moderator Isimmo]
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Old 07-09-21, 08:01 PM   #2
mikes2
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It's not a relay. It's a control unit.

On the MB it will likely be under the rear seat
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Old 07-09-21, 09:13 PM   #3
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Default J178 relay for diff lock. MB quattro

Thanks-but it is not under the rear seat-although Phil Payne site says it is.

There is a different electronic unit there with only two wires which I think is the acceleration sensor.
Black/blue
Black/green

I Wonder if he meant under the car, under the seat. I am not certain I understand the mechanics of the MB diff lock. I cannot glean much from the literature!

Maybe Friday will bring enlightenment, but any clues welcomed.




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Old 07-09-21, 10:24 PM   #4
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Pretty sure that's where it was on mine as I had trouble with it and had to replace it.

893 919 173

From the rear diff vacuum unit, you have two vacuum pipes that go up into the car. One has a yellow stripe and the other has a blue stripe.

Follow them and you'll find it unless it's been removed.

There's also a lilac vacuum line which comes from the front of the car (inlet manifold)

There's a 5 pin connector. Wires will be

blue / white
blue / black
brown yellow
black / yellow
brown

same part used on later cars and there's a wiring diagram available here

http://s2-audi.co.uk/workshop/schema...lock/page2.png
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Old 07-09-21, 10:26 PM   #5
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Thank you Mike. That is brilliant and very helpful.
It is tempting to go and check now, but probably best left until Friday!



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Old 07-09-21, 11:06 PM   #6
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Found it.
In the boot, behind the spare wheel, behind the trim on the side of the car.
Currently unplugged, and I suspect the actuator under the car needs to be exercised a little, with some WD 40 for good measure.
Cheers!



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Old 10-09-21, 04:31 PM   #7
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Default J187 relay for diff lock. MB quattro

The Problem seems to be a split in the plastic vacuum part.
I could hear a puff of escaping air when I moved the arm in and out manually.

I Couldn’t get the vac part off and had nothing to put back on if I did so gave that up for today.
I will get one of the merc parts and fix it another time.
No rush there

I Also need to get the sensor out as it appears to be jammed showing the diff to be on whether it is or not.

I reconnected and then disconnected the sensor plug which had been cable tied to one side, because the Diff locked warning light came on-regardless of whether the diff was locked or not-and this also switches the ABS off.



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Old 10-09-21, 08:13 PM   #8
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The rear diff lock automatically disengages at 25km/h (15mph).

That function can be bypassed by cutting the blue / white wire. Just check that your blue / white wire is intact.
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Old 10-09-21, 10:55 PM   #9
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Quote:
Originally Posted by mikes2 View Post
The rear diff lock automatically disengages at 25km/h (15mph).



That function can be bypassed by cutting the blue / white wire. Just check that your blue / white wire is intact.


Cheers Mike. That’s good to know.

I’ve tidied my post up a a bit as it didn’t read well. Hopefully clearer now.


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Old 11-09-21, 01:07 PM   #10
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If you've got a mityvac or similar you can mimic the actuator to engage and disengage.

Sounds to me like the rear diff locking arm is stuck.

The switch in the diff is just a ball that pushes in or out to engage/ disengage so when the actuator moves, the arm inside the diff pushes on the switch which will then turn on the light.
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