W124 Overvoltage relay makes rattling sound = no good?

[JensenHealey]

Hello all:
I have a 1993 300TE with the 3.2L engine and the ABS light is on constantly. I have pulled the overvoltage protection relay out of it's socket next to the battery and when I shake it, I can hear a rattling sound inside the relay. After doing some research I found a statement on another Mercedes-Benz forum that if the OVP relay rattles like this it is no good and should be replaced. Can anyone here confirm that?

Thanks
--
Steve

 

[grober]

THE OVP SUPPLIES THE ABS UNIT, THE MOTORISED IDLE VALVE AND ENGINE ECU --IF THE ABS LIGHT IS ON AND THE OVP IS RATTLING REPLACE IT- THEY CAN SOMETIMES BE REPAIRED BY RESOLDERING BUT ITS A LOT OF HASSLE

 

[Habil]

Yes you can open it but it's a bit difficult. Have you checked the fuse is in place on top of the relay?

 

[JensenHealey]

Yes, I checked the fuse and it is fine.

 

[Habil]

I have opened one about a month ago but haven't got any pics. I could try to explain how to open it if you want to resolder it.

 

[JensenHealey]

Sure, any information would be helpful.
Thanks
--
Steve

 

[grober]

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[optimusprime]

I would purchase a new one .Then operate on the old one repair it if possible, and keep it for spare .

 

[Habil]

You can test the relay as explained in the linked thread.

OVP - basic function and test

www.benzworld.org

To open the relay you need to uncrimp the metal casing along the edge at the plug end and pull the circuit board out, I used a pair of pliers on one of the pins. Also remove the fuse first.

I can't upload any pics, because there to big, I will try tomorrow from my computer

 

[JensenHealey]

Thanks, I got the relay open.
I found a video on youtube where the person claims that if the OVP relay fails on a mid-1990's E320 that the car will not start.
This is not the condition I have so I am wondering if this is true or not.

 

[grober]

THE OVP is multistage the coil/contact that protects the ABS unit is different [pin7] to the ECU one.
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/E320/SYSTEM WIRING DIAGRAMS/5418.pdf
and

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/E320/SYSTEM%20WIRING%20DIAGRAMS/5410.pdf

 

[ChipChop]

OVP relays are dead easy to resolder, you literally just need to dab the bad contacts with a hot iron and they should be good again. Opening it up is harder than the soldering imho.

 

[Will]

Dry solder joints won’t cause it to rattle though?

 

[JensenHealey]

Yeah, after taking the relay apart I think the rattling was the plastic inner liner pieces.
I also tested on the car after taking the cover off and all three relay coils are pulling down the contact plates when the ignition is energized.
I am going to do some more research to see what else could cause the ABS light to stay on constantly just in case the problem is not really within the OVP relay.

 

[Habil]

The plastic inner liner pieces shouldn't move around. They sort of insulate the circuit board from the metal casing.

Also there could be hairline cracks in the solder joints witch are only visible below a magnifying glass.

Also even though the relay coils are pulling down the contact plates you need to check that there is an output at the correct pins. Is it a 6 pin relay?

 

[grober]

http://www.diakom.ru/CARS2/pribor/cs1000/manual/cs1000_mb.pdf
page 58
Most likely cause of the ABS light coming on [ if not ovp related]is a fault is with one of frontwheels /rear diff speed sensors or their wiring. A simple blink code tester should be able to narrow it down.
e.g.

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[JensenHealey]

Thanks again Grober for the excellent reference.
I looked at that cs1000_mb.pdf manual and I see the listing for the 16 pole diagnostics connector which is what my W124 car has.
On page 11 of the file is a list of the various outputs with the purpose of each port in the diagnostics connector but I do not see anything there that talks about ABS system faults.
Am I missing something?

 

[Habil]

Most likely cause of the ABS light coming on [ if not ovp related]is a fault is with one of frontwheels /rear diff speed sensors or their wiring.

If it was a problem with the sensors wouldn't it only show up after moving the car? On my W124 250TE the ABS light turns on only after moving, and I suspect it's the sensors.

Thanks again Grober for the excellent reference.
I looked at that cs1000_mb.pdf manual and I see the listing for the 16 pole diagnostics connector which is what my W124 car has.
On page 11 of the file is a list of the various outputs with the purpose of each port in the diagnostics connector but I do not see anything there that talks about ABS system faults.
Am I missing something?

On page 58 are the codes for the ABS.

 

[grober]

No you are correct the 16 pin connector does not appear to have a socket 6 dedicated to ABS like the 38 pin one has
However the ASD AND 4 MATIC systems pages 52,56 use the self same wheel sensors and can be monitored at socket 5
might be worth a try?