ABS - 1993 220E (facelift)

[David124T]

The ABS warning light on my 220E estate comes on when the car starts to be driven (it goes out when the engine is first started).
I have done/checked the following:

Battery fully charged
Cleaned all three sensors/senders
Checked the OVP fuse is OK
Cleaned the pins on the OVP relay

Are there any other checks that I can do before I start replacing parts?
The whole system appears to be Bosch. Can I get the parts from them or do I have to go to a dealer?
If I need to start replacing parts, I was going to do so in this order (cheapest first)
OVP relay - approx £50 +VAT from MB
Each sensor in turn - approx £98 +VAT each from MB
Thanks for any suggestions/advice.

David

 

[television]

This will not be the OVP it will be a wheel sensor, its normally the fronts but it could be any one

You could take them out and clean them

 

[David124T]

Malcolm,

Thanks for your post.
I have already removed and cleaned all three sensors/sendors.
I am of the opinion that I need to start buying new parts unless you can suggest otherwise.
As usaual, I am grateful for any suggestions/advice.

David

 

[bigasotonuk]

Hi,
I have heard that you can measure the resistance (multi-meter set on ohms) across the wheel sensors this will tell you which one it is but what the resistance should be i don,t know.
You could try measuring them and see if one of the measurements varies greatly from the others, that could be a starting point.

 

[David124T]

Hi Andy,
I have also heard/seen that solution.
I think that i am past that point.
Unless someone has any suggestions, I will be ordering a new OVP relay.
The MOT is looming and although I could disconnect the ABS to get the car thru, it is not my style. I want the car right.
I suppose my real quesion is can I get the parts from Bosch (hopefully cheaper) or do I have to go to a dealer?
I have posted the price of the parts that I think I need. I don't know if the order of replacement parts I have posted is right or not. That is the advice I am seeking.
Thanks
David

 

[television]

Why not measure the voltage on the OVP relay there should be 12volts in pins 87

 

[David124T]

Hi Malcolm,

I am sure you remember my thread about probes and where to stick it.
Can you talk me through it please.
Thanks
David

 

[television]

The ABS works like this.
When you turn on the ignition, if the OVP was faulty the low voltage would turn the lamp on, and it would stay on when you started the car. If the OVP was good, the lamp will go out when you start the car. If you drive the car and the lamp comes on it will be a sensor.

The ABS module has a built in clock comparator, the speed of the road wheels via the sensors, send the pules back to the comparator, if one wheel is not counting or sending pulses then it shuts down the ABS pump, as a safety precaution.

The reason 90% of the time is dirty or faulty front sensor, the cables can break etc, some cars only have one sensor for the rear.

A simple meter to compare them will give the answer

 

[television]

Hi Malcolm,

I am sure you remember my thread about probes and where to stick it.
Can you talk me through it please.
Thanks
David

Can you find the old thread

If you mean the OVP relay, getting to the pins can be difficult, its easy with the cover on the relay removed as you can get to the pins.

 

[David124T]

Hi Malcolm,
Sounds like you are discounting the OVP as at fault.
I have had all the senders out to clean them but the ABS warning light still comes on.
How do I test the sensors?
Please bear in mind that I don't have any instructions with my multimeter.
Thanks
David

 

[television]

Hi Malcolm,
Sounds like you are discounting the OVP as at fault.
I have had all the senders out to clean them but the ABS warning light still comes on.
How do I test the sensors?
Please bear in mind that I don't have any instructions with my multimeter.
Thanks
David

On the ohms 200 range, just put the leads on th 2 pins in the sensor or unplug the sensors where they plug into the abs pump, thats easier, just measure all three or four and see if one is giving a much higher or no reading than the others

This will be the one that has gone

 

[David124T]

Hi Malcolm,
Thanks for the advice. I haven't come across that test in any previous post before.
I will let you know what I find.
Thanks again

David

 

[David124T]

Erm, just got out my multimeter. It has 2 ohm settings. X10 and X1K.
Which one should I set it to? (said you would have to talk me through it, sorry)
David

 

[David124T]

On the ohms 200 range, just put the leads on th 2 pins in the sensor or unplug the sensors where they plug into the abs pump, thats easier, just measure all three or four and see if one is giving a much higher or no reading than the others

This will be the one that has gone

Finally got the car off the wife so I can do this test.
I have attached an image (hopefully) of the ABS wiring socket.
The pin sockets are numbered (as seen in the photo) like this:
2 1
4 3
6 5
8 7
10 9
12 11

Number 8 is a blank

Can anyone tell me which sockets relate to which sender and which one's I should measure.

Thanks

David