1985 SL280 ABS fault codes? - PeachParts Mercedes-Benz Forum

woolf · #1 08-19-2006, 12:29 PM

Hi guys,

I thought I'd bought a car with ABS until I locked it up on wet roads yesterday. On investigation I found that the ABS warning bulb was missing

I've now fitted a bulb on surprise surprise it stays on all the time

Before I start pulling everything apart, is there a way of retrieving the fault codes from the ABS ECU so that I can get a clue where to start?

Many thanks
John

ctaylor738 · #2 08-19-2006, 02:00 PM

Not that I know of. With the light on all the time, the first thing I would look at is if the unit is getting power.

woolf · #3 08-20-2006, 10:03 AM

Quote:

Originally Posted by ctaylor738

Not that I know of. With the light on all the time, the first thing I would look at is if the unit is getting power.

Thanks for the reply, and for the starting place

I just checked and can't find 12V on any of the ABS ECU pins, although one of them is showing 2V.

I haven't found any defective fuses, so where could the power be going missing?

ctaylor738 · #4 08-21-2006, 09:48 AM

Unfortunately, I have only the basic wiring diagram for the 280SL, and it does not include the ABS. You would probably be able to find it on a UK model CD or manual.

But I did find something for a 1985 380SL on the US CD. The ABS does not get it's power from a fuse. There is a relay in the "relay farm" in the right footwell above the fuse panel which supplies power to the ECU, and there is an Overprotection (OVP) relay which feeds it. But the wiring diagram only shows the OVP relay. So you are going to have to look and see what your car actually has.

But here is what you can check. If it is like the US setup, you should see 12V at the ECU on a black wire (from OVP) with with ignition on, and 12V on the blue/red wire with the engine running (output from alternator).

I would start with the fuse on the OVP.

Your 2V reading could come from a bad OVP or the other relay, or a corroded wire or connections.

woolf · #5 08-21-2006, 01:49 PM

I think we're getting warmer...

The pin with only 2V with ignition on, changes to 14V with the engine running. There are no other terminals with voltage.

So I now need to find where the 12V to the black wire is supposed to come from. I've removed the kick panel but I can't see any fused relays in the "relay farm". I've identified all the relays apart from the 4 identical standard looking ones, which I doubt have anything to do with OVP.

Many thanks for your help, I feel I'm getting closer.

ctaylor738 · #6 08-21-2006, 04:03 PM

The OVP on your car may not have a fuse. On a 1981 380 that I worked on, the OVP was a red "ice cube" type. The OVP in my diagram has two power feeds: pin 8 from fuse 7 black/red wire (hot in start or run), and pin 1 from battery red wire (hot at all times).

woolf · #7 08-28-2006, 06:31 PM

Quote:

Originally Posted by ctaylor738

The OVP on your car may not have a fuse. On a 1981 380 that I worked on, the OVP was a red "ice cube" type. The OVP in my diagram has two power feeds: pin 8 from fuse 7 black/red wire (hot in start or run), and pin 1 from battery red wire (hot at all times).

Thanks for the information. I haven't found a relay that matches your description, so I rang my dealer to try and order an OVP and they were adamant that my chassis number didn't have one.

It would make life so much easier if wiring diagrams were available