W124 ASD strange problem

[Andarcomodante]

300TE auto

I have a little problem with it and was hoping for some advice.

Yesterday morning the ASD light came on and stayed on and when I press the break pedal I get a rapid clicking noise from the dash area and the rev clock, oil pressure guage and fuel guage all drop to zero, also the seatbelt warning light comes on for a few seconds.

I have heard that the engine harness can deteriorate and cause strange problems, but am not sure if this was US market only models?

Any tips would be greatly appreciated before I give it the crrippling expensive and hugely incompetent Mercedes dealer here.

Many Thanks in advance.

 

[Will]

Not sure exactly what/why you're experiencing clicking behind the dashboard, but I have had two faulty brake light switches on ASD equipped 201 cars (almost identical to 124 setup), so bearing in kind that the light has come on and it's linked to you operating the brake pedal, I would start by checking that. Very cheap and easy to replace if needed

 

[Andarcomodante]

OK, thanks for that. What is the ASD by the way?

 

[Will]

BTW, I posted up on here a while back how to read the fault codes for the ASD system from the diagnostic connector in the engine bay.

On a RHD W124 it will be located near the bulkhead, by the brake master cylinder.

 

[Will]

OK, thanks for that. What is the ASD by the way?

ASD is a system that controls the locking for the rear differential. It gives better traction on poor surfaces or when accelerating quickly.

 

[Andarcomodante]

That what I thought, but someone else told me it was only on 4 wheel drive models!!

 

[grober]

irrc there is a very large earthing point behind the instrument cluster. If you have a leaking windscreen for example that may have been compromised. I suggest you pull the cluster out and have a look at the instructions here\:- PeachPartsWiki: Instrument Cluster Removal THATS after you have tried Wills solution with the brake light switch which is a good one.

 

[Will]

That what I thought, but someone else told me it was only on 4 wheel drive models!!

That isn't correct!

 

[grober]

The other possibility is a faulty OVP relay which supplies the ABS/ASD unit-- sounds as if your problem is electrically based rather than anything else-- try Will's brake switch suggestion first.

 

[Andarcomodante]

Cheers guys,

have just disconnected the brake light switch (how many wires!), the ADS light is still on, but the problem of the guages dropping to zero and the clicking noise has gone, so it isnt that, its just not happening as the circuit isnt being mad whne i press the brake, I'll try the other thing now.

 

[Andarcomodante]

Erm, i understand the OVP relay is very easy to change, but.... where the hell is it?

 

[Will]

Is the ASD warning lamp constantly lit?

If so, you need to read the fault codes from the diagnostic connector to see why it is lit, it is illuminated for a reason - to indicate a fault (or perceived fault!) in the system

Here's a quick guide I made for the W201 series cars, it is be same for your W124 except for that your diagnostic connector is on the driver's side as I mentioned earlier

http://www.mbclub.co.uk/forums/571881-post13.html

HTH,

Will

 

[GP801]

The OVP relay is behind the battery. Its the one with the fuse on top

 

[Andarcomodante]

Cheers! we are getting there. Found and removed the OVP relay, looks Ok, no corrosion on contacts. There is also a box marker ASD, could it be this?

I will be trying Wills diagnostic trick, see what that comes up with.

 

[carat 3.6]

I had the exact same problem with my e300 diesel, it turned out to be a bad earth to the light control unit.

I think the thread was called "w124 electrical sillyness".

 

[Andarcomodante]

Thanks for all that guys. Turns out it was a dry joint on the pcb of the OVP relay, resoldered the connections and all is good. Thanks to Will for his tip on how to reset the ASD light. Now have another problem but thats for a different section!