ABS Light
 

1988 260E

A couple weeks ago I noticed the ABS light was aglow on my kid's daily driver. Well, I took it for a spin but noticed the light ONLY comes on after it is started AND when the brake pedal was depressed. It will remain on until the key is turned off. Once again, after start up, when the brake pedal is depressed - *POW* - ABS light! I just replaced my OVP with a new one and was hoping upon hope it would remedy it, SRS light, and my "light bulb out" warning light. But no. Any ideas?

The abs system is somewhat basic. Start at the wheel speed sensors and work your way in. There are 3 total. One on each front wheel and one on the rear differential

How would I go about testing them? With multi-meter?

Don't quote me, but I believe they are Hall effect sensors. Trace the wire in to the engine compartment, you will find a plug. There should be a reading of " x" ohms, and when you spin a he wheel that value should fluctuate.

Someone with a service manual can chime in with the specific readings.

If the abs turns on on the first press of the brake pedal I'd be looking for a broken wire, or something a bit more obvious.

I've had this problem with my ABS before too. First, if key is turned on and before the car even starts moving, if the ABS comes on and doesn't go off, check the OVP. IF the car moves and the light comes on check the wiring from the wheel hubs (usually the front) to the plugs in the engine bay near the wheel well. Check for continuity, I forget the values, but unplug the connectors and check resistance on the actual sensor by placing one lead in the center female opening, and the other lead on the part just outside the inner opening, but still within the connector. I think its something like 1.1, at least this is the case of my 201.

Yesterday, I installed a brand new OVP. I was disappointed that the ABS light popped on after starting it up and touching the brake pedal. I took a chance since the old OVP was possibly the original.

If this was my first experience of MB ownership, it's likely I'd never own another. But my other two cars before this (one of which is our DD) are/were exactly the opposite. I couldn't ask for better service from them, but not so much the story with this 260E!

So far several people have ruled out the OVP as the issue and suggested tracing the wiring and finding the root-cause for the fault (the light is telling you there's a problem in the system). So far the OVP has been replaced (even though it was fine), but the wiring hasn't been checked. The car is at least 28 years old and things fail regardless of who owns them and how well they're cared for. How is this the car's fault again?

The matter of quoting is inevitable; but the sensors are not Hall type, they are simply two-wire, magnetic, inductive pickups, aka VR sensors. There should be conductivity through the two wires.
Fronts: .85 - 2.3 Kohms
Rear: .6 - 1.6 Kohms

Well, first of all, I'm not 'blaming' the car! I just simply have a low tolerance for 'stuff' being wrong with my car especially electrical gremlins. I have better things to do with my time.

I've already spent more time than I'll ever recover from reading thread after thread after thread of similar symptoms for glowing lights on the dash panel. Standing by my comment that I would likely not own another MB IF I HADN'T HAD SUCH GOOD FORTUNE WITH TWO PREVIOUSLY ACQUIRED CARS.

Thank you for this info, when I have the time to get into it, I'm sure it will prove useful.

Another thing you should do is pull the sensors from the hubs and clean the tips. Because they are magnetic, they tend to pick up iron filings and metallic debris, which screws up the system.

Correction is due on that one. I was going off the top of my head on a very foggy memory of my abs troubles many years ago.

Bottom line is that you should get some reading of resistance when tested. Likely one of them is very dirty, or an obvious broken wire. Should be pretty easy to track down.

I agree with Diseasel300, you've stated you replaced the OVP which did not help, the next logical step would be to trace the wiring. There is maybe 2ft of wiring each at the front sensors, which is where the problem is likely at. Your long battle with the abs light may have been resolved within 30 mins - 1 hr of actual physical work on your end. If a glowing ABS light frustrates you to the point where you've made the decision to never own another MB again, I'd hate to see you having a rough idle/hard start issue :D. If it turns out one of your sensors is toast, I may have an extra that I could send you (front sensor only).

Ohh gosh, rough idle and hard start issues are what define my hatred of CIS, only had my engine running 100% correctly for 3 weeks before something else failed and the system went haywire.

But I agree, remove the sensors and clean them off, that would be my first step as it's incredibly easy and should be done as regular maintenance.