ASD/ABS Problems... Please Help

Cossie 2.5

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Jul 5, 2004
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190E 2.5-16
HELP...!! I've got a 2.5 16V 190 and there is an intermittent problem with the ASD and ABS (it appears to be linked). Please bear with me as I attempt to describe it.... In essence there are 2 symptoms.. 1st is that when moving at parking speeds (forward or reverse) the ASD warning triangle lights up and the diff locks resulting in nasty clanking noises which sounds like the plates locking in the diff, the other is that at standstill when I rev the car I can feel a lot of feedback through the brake pedal (like the ABS working). Very occasionally the ABS warning light comes on and then once I've turned the car off and started it again the ABS light is not on anymore!
Now... I've removed the sensors from the front wheels and cleaned them and have tested them for a signal and they appear to be fine. When I remove the ASD relay (from near the battery) the locking of the diff stops but the feedback through the brake pedal remains!?? Have also done a fault test on the ASD and it indicates no fault!! I am at a loss of what to do to be honest... I'm tempted to replace the ASD relay but cannot imagine why that would fix it so am reluctant to spend the money on the off chance... can ANYONE PLEASE help me with some info.....??
Thanks...
 

Will

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What about the OVP relay? Common fault on 80's MBs. Can't comment about the ASD in particular, but I know that it would be a likely culprit for some ABS issues (the sensors near the wheels being another, but you've checked those...)

Worth checking? :)

Will
 

Per Eriksson

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Nov 21, 2004
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Make sure the tires match in size and wear front and back also.
 
OP
OP
C

Cossie 2.5

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Joined
Jul 5, 2004
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Location
Berkshire UK
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190E 2.5-16
Will.... what about the OVP relay.... please expand.... where is it, what might I check with it etc... This problem is driving me nuts! The ABS warning light came on last night and when I tested it with an emergency stop the ABS wasn't working, however once I'd turned the car off and back on again the ABS light had gone off and the ABS was working again!!! The warning triangle and the locking Diff is happening constantly but only at very slow speeds, parking, traffic jams etc... it seems to be worse when turning (reverse parking etc)...... HELP!! :confused: :eek:
 

guydewdney

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the OVP (over voltage protection relay) often goes belly up - resulting in all sorts of odd things happening. Have you got a decent multimeter? connect to battery and monitor voltage... I have found that bad earths / connections on other vehicles (bikes mostly) that the voltage is OK at tickover, silly at slight revving, and then 'normal' at high revving - so 1) check all battery / earth connections and 2) check / replace the OVP relay.

The ABS wont work if it sees a fault - it has no point of reference it can rely on - so it does the 'safe' thing and disengages.

What about checking the REAR sensors? you say you have checked / cleand the fronts, but not the rears? they are just as important...
 

Will

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Hi Cossie 2.5,

The OVP relay is situated behind a plastic panel which is behind the battery. From what I remember it is aluminium cased and about an inch square and a couple of inches tall. It has a clear plastic cover on the top containing a regular blade type fuse. Might be worth popping it out, checking the contacts are clean, checking the fuse etc. Failing that, do you know anyone else who you could substitute your one with? Would only take a few seconds to swap over.

I think one of the tests (if it has failed completely!) is whether the ABS warning light will come on (at switch on) and go off as soon as your vehicle is started (which it is supposed to do). Obviously if you have an intermittant fault this might not show up.

Good Luck, :)

Will
 

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