w126 560 SEC abs fault

[Chris560SEC]

I have a fault with the ABS on my 560SEC.

Let me describe the fault in detail.

When starting the car and moving off you can feel the abs pulsating through the pedal at light brake pressure applications. I can feel some resistance to the pedal that I "push" through to activate the brakes efficiently. This happens until you reach 30mph when the ABS light comes on and the normal feel returns to the brake pedal.

The car has been looked at by two auto electricians. The first replaced the rear abs sensor as it was "reading low voltage". The second hooked up the system to an oscilloscope and tested each unit in turn. The voltage readings were fine, however he was only checking at low speed as he hand rotated the wheels.

I had hoped the auto electrician would read off the pins on the abs ecu to see what was happening but it seems the data for this age of car is hard to come by.

The auto electician cleaned each unit but could not remove the O/S/F as it would not budge and he feared it may break.

Short of replacing the front sensors at £80 each, do I have a diy solution that I can consider to get my abs working and the MOT passed!

I have a good understanding of the car but little hands on experience as it is normally so damn reliable. 30k miles in the last twelve months.

Thanks for your help

 

[television]

If the pump is being modulated when the pedal has not been pushed, this would not seam to be a sensor fault as they are in the primary circuit, do you have the full 12 volt going to the pump control module item 62 in the link.

You should also make sure that the OVP relay is in good order and that you have 12volt on pins 87 these units can be intermitant



http://www.detali.ru/cat/oem_mb2.as...&L=765.706&CT=F&cat=569&SID=54&SGR=075&SGN=04

 

[Chris560SEC]

Thanks Malcolm,

The abs is activated as I touch the brakes at the low speeds below thirty.

I know where the OVP is near the firewall and with a 10A fuse on top. Do they often cause the fault I describe?

Chris

 

[television]

Thanks Malcolm,

The abs is activated as I touch the brakes at the low speeds below thirty.

I know where the OVP is near the firewall and with a 10A fuse on top. Do they often cause the fault I describe?

Chris

Hi Chris, yes the OVP relay is known for ABS problems in that they were all badly soldered up, I think that the Irish ones were better than the Austrian.

I cannot say that this is the problem, only by doing a voltage check will tell. There should be 12v on pin 30 and 12v on pins 87

Any pin 30 on the ABS pump must have 12volt

Always start with basics

 

[Chris560SEC]

I will check the OVP

Thank you for steering me in the right direction.

I will check the OVP and revert on Thursday evening.

Thanks Malcolm.

 

[Chris560SEC]

There should be 12v on pin 30 and 12v on pins 87

You will have to excuse me for being a little ignorant on matters electrical!

I have just had a look under the bonnet. Where exactly should I be looking for pin 30 and pin 87 in order to test for 12v.

I gave it ten minutes then came in to own up that I don't know!!

Regards,


Chris

 

[television]

You will have to excuse me for being a little ignorant on matters electrical!

I have just had a look under the bonnet. Where exactly should I be looking for pin 30 and pin 87 in order to test for 12v.

I gave it ten minutes then came in to own up that I don't know!!

Regards,


Chris

If you pull the relays out, they have numbers on the pins

 

[Chris560SEC]

Thanks Malcolm

I figured it might be obvious

Regards, Chris

 

[Chris560SEC]

W126 Ovp - Abs Problem

I have now changed the OVP.

The symptoms have changed slightly. Now the ABS light comes on from 5 mph as I accelerate but the abs activation has ceased at low speeds that was happening before I changed the OVP!

Any ideas where I should now be looking?

Thanks,



Chris

 

[television]

OK you have a volt meter, do check the running voltage as the ABS runs from the alternator and not the battery, the running voltage should be 13.8 volt, if this is correct then it should just be a wheel sensor at fault

 

[Chris560SEC]

560 Sec

Thank you Malcolm,

your encyclopedic knowledge is much appreciated!

I will have a look on Thursday and finally nail the problem.

Regards,


Chris

 

[television]

After that it is a matter of checking the wheels sensors maybe just cleaning them

 

[Baracuddda]

W126 abs light on

Hello All my 1988 SEC500 has developed a fault whereby the ABS warning light stays on all the time. It used to come on and go off but now its permanently on.
Any suggestions welcome.
Could it be low voltage ? And how does a simpleton check that.

Many thanks