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Old 21-03-2013, 04:50 PM   #1
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W124 ASD light, diagnostic help please

The ASD light (lower right hand side of dash) has been on for a few weeks now.

It used to come on for an hour or so after a car wash and then turn itself off. The last time this happened, each time I pressed the brake pedal, another light would come on in the middle of the dash too. Now the ASD light stays on all the time.

I found some threads which describe using a wire between terminals 1&5 in order to get a flashing code to locate the fault, but the light still stays on and there is no flashing. I really dont want to just go out and get a new ASD relay as they are expensive, but is there anything else I can do to get the diagnostic to work?
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Old 21-03-2013, 06:32 PM   #2
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Clean ABS sensors on the wheels,
Low battery voltage,
Brake light switch can do this too.
You also need a little bit of slack on the throttle cable, has anyone been near it lately...?
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Old 21-03-2013, 06:40 PM   #3
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You need to read the fault code when the ASD light is on.

I posted up a how to for this somewhere on here, I'll see if I can find it for you
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Old 21-03-2013, 06:43 PM   #4
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jazzdude

Do you mean ASD, as that is a limited slip diff normally found on diesel 124 ?

Do you mean ABS brakes ?

OR do you mean ASR (anti slip regulation) which features drive by wire electronic throttle linkage instead of a throttle cable.?
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Old 21-03-2013, 09:20 PM   #5
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I mean the ASD light only, no ABS or triangle. It is a yellow rectangular light in the strip along the bottom of the instrument console, at the far right.

For some reason, when I put the wire in ports 1 & 5, nothing happens, the light just stays on.
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Old 21-03-2013, 09:29 PM   #6
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Check continuity between pin 1 and ground - or just ground pin 5 to chassis or battery earth?

You have to short pin 5 to ground for approx 1 second and then release. It should then flash accordingly.

If this still does not work I guess you have a more serious fault.
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Old 21-03-2013, 09:43 PM   #7
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so if I get a longer wire, connect one end to port 5, and the other say to the bodywork, it should flash after a second.

If not, then could it be the ASD unit itself?
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Old 21-03-2013, 10:01 PM   #8
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Quote:
Originally Posted by jazzdude View Post
so if I get a longer wire, connect one end to port 5, and the other say to the bodywork, it should flash after a second.

If not, then could it be the ASD unit itself?
Yes - you could run a longer wire from pin 5 to where you can actually see the lamp (and ground it to something like the door catch on the B-pillar)

Otherwise I can't see how you know the light doesn't flash at all unless you have an assistant shorting the wire out for you
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Old 21-03-2013, 10:09 PM   #9
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Thanks, I will give that a try
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Old 21-03-2013, 10:31 PM   #10
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I think you may have the ASR system rather than the ASD but without seeing the car?? The ASR 2 control unit is supplied by the OVP relay which often gives problems?
The abs/asr fault codes to be found on pin 5 are below.

Last edited by grober; 21-05-2013 at 09:48 PM.
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Old 22-03-2013, 02:41 PM   #11
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I tried to put one end of a wire in port 5 and touched the other end to an earth point. Nothing happened.

I then tried looking for the OVP relay and was prodding around the area where the ASD relay sits. The next time I started the car, the ASD light turned off.

I do not have a clue if this is coincidence or I did something but even if it is, I am still concerned that I could not get the diagnostic sequence to work.

By the way, I thought the OVP relay would be next to the ASD relay, with the OSD relay with its long edge parallel with the windscreen. What I did find was the ASD relay parallel to the SIDE of the car, and a black box behind it. Is that the OVP relay?
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Old 22-03-2013, 03:05 PM   #12
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Here is a circuit for a fault code reader. After you have built it- parts available from your nearest Maplins Find the permanent 12v live in the diagnostic socket---- find the constant earth ---- connect the yellow plug to pin 5

With the ignition ON !!!!! press the "momentary switch" to start the fault code sequence.

ps The OVP relay is often covered by a black cover its easily identified with the cover off as it has either one or more often two fuses on the top.
pps this is a very useful site http://web.archive.org/web/200903220...om/MB_X11.html
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Last edited by grober; 20-09-2013 at 09:34 PM.
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Old 22-03-2013, 03:08 PM   #13
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Relay locations and wiring diagram, if it helps?

OVP is behind the battery on my 300TD
Attached Images
File Type: jpg relays.JPG (118.2 KB, 10 views)
File Type: jpg asd.JPG (153.8 KB, 12 views)

Last edited by balge; 22-03-2013 at 03:09 PM. Reason: ovp
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Old 22-03-2013, 03:23 PM   #14
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The mechanic had a handheld 'reader' with an LCD screen and three banana plugs on it.

He initially connected it to the diagnostic pad, I didn't see which holes he used though, but said that for some reason it was not connecting to the ECU.

Can this device be used to diagnose the ACD?

But with the light off now, do I have to wait for it to come back on again to try this?
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Old 22-03-2013, 05:43 PM   #15
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Its almost always the ASD relay... they are a pain...
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