ABS light coming on

[400bonus]

I have a 1989 190E approx 60.000mls after moving about 1/2 mile there is a noise of the ABS cutting in, the brake pedal seems to move away from me and the ABS warning light comes on any ideas ?

 

[wireman]

There is nothing in the system that would pull down the pedal, in fact the reverse occurs when the ABS pump engages and it should not be able move back up since the master cylinder piston is in the fully home position. Make sure the brake pedal is returning fully to its stop.

Check the wires from the 3 sensors, the front ones are on the hubs the rear one is on the nose of the diff. there is a cable break connector near the suspension strut top (under the bonnet) on each front sensor make sure these are OK. Once you know what these look like find the one on the back end and check that, it may be beneath the seat.

The front sensors phonic wheels (a gear toothed afair on the hub itself) can rust away and cause trouble, remove the sensors and inspect them through the mounting holes, if the teeth are rusted away you need new hubs.
The rear sensor is in oil and won't rust.

The clever bit is behind the battery alongside the over voltage relay, check that there is no water damage around these, the OVP relay seems to be a common trouble spot so have a look around the forum for this. On my 124 it has a small black cover over the OVP remove this and check the fuse on the top of the relay.

There are two relays on the pump unit remove the black cover and check them for water damage and that they are in their sockets etc.

Check all the cables you can find that go to the various parts of the system make sure that non of them are damaged by abrasion or pulling.