W202 '96 ABS - Brake switch or sensor

[Ellis]

I've had an the ABS light intermittently coming on/off, when the light is off I've noticed that the ABS cuts in very early, just normal braking, is this likely to be the sensor (what is correct name for this part please ) more than the brake switch.

If it is the sensor is there anyway to tell which side it is without paying for a diagnostic?

Thanks


Ellis

 

[Iain]

I had a similar problem with my car, except the abs light was on continuously and the speedo wasn't working. I replaced the brake light switch (£7) No change. I then went to the local knowledgable auto elec. who went straight to the OVP relay. That was open circuit. Replaced this and all is now well.
Perhaps later, Malcolm (television) will be on and shed a bit more light on this subject. I seem to remember that he mentioned this in a previous post, that the relay contacts can go 'dry jointed'.
If it turns out to be the abs sensor, pm me as I have a brand new one spare. I'll have to check which side though as the fronts are handed and there is probably only the one on the rear axle.
You could try removing them on the front and then cleaning before re-assembly.They get a build up of swarf-like material on the face which could be responsible for your erratic performance.
Hope this helps.

 

[Ellis]

I had a similar problem with my car, except the abs light was on continuously and the speedo wasn't working. I replaced the brake light switch (£7) No change. I then went to the local knowledgable auto elec. who went straight to the OVP relay. That was open circuit. Replaced this and all is now well.
Perhaps later, Malcolm (television) will be on and shed a bit more light on this subject. I seem to remember that he mentioned this in a previous post, that the relay contacts can go 'dry jointed'.
If it turns out to be the abs sensor, pm me as I have a brand new one spare. I'll have to check which side though as the fronts are handed and there is probably only the one on the rear axle.
You could try removing them on the front and then cleaning before re-assembly.They get a build up of swarf-like material on the face which could be responsible for your erratic performance.
Hope this helps.

Thanks for the info, what is the OVP Relay, where is it and how much? Do you think I should try this before brake switch and sensor checks.

Anyone know if these sensors are covered in Haynes, easy DIY job?

Thanks

 

[Iain]

Thanks for the info, what is the OVP Relay, where is it and how much? Do you think I should try this before brake switch and sensor checks.

Anyone know if these sensors are covered in Haynes, easy DIY job?

Thanks

The sensors are dead easy to take out. 1 x 10mm socket is all that is required. The OVP relay should be located under the cover adjacent to the ECU. Bulkhead passenger side. The OVP is the square relay with the fuse on top under a plastic cover.


OVP= over voltage protection

 

[Rod Adams]

Before you buy any new bits, it may be worth taking out the ABS sensors and giving them a clean. I had similar problem to you on my W126. When I took the sensors out they were covered in black gunge. Probably a mix of steel grindings off the brake disk and god knows what. Anyway, cleaned them up and problem fixed.

Cheers,

Rod.

 

[strikemaster]

I have just had the same fault. ABS light on permanently and speedo inop.

Went straight to the relay after reading the above advice and found the fuse had gone. Replaced it and both faults disappeared.

Interestingly, the Merc computer showed the switch was inop....