Replaced ABS sensor but light is still on? - PeachParts Mercedes-Benz Forum

Fulcrum525 · #1 07-04-2009, 03:08 PM

Last year I replaced my left front ABS sensor and my light went out for a few weeks but then started coming and going out every time I started to drive. (The light would only come on after I drove for a few miles) I just got through putting a brand new sensor on the right side and now the light comes on the second I turn the car on and stays on (did a 4 mile test drive and it wouldn't go off even after I restarted the car) Is there another method to reset the system or is something else wrong here?

nhdoc · #2 07-04-2009, 03:22 PM

I know on the early ABS systems they had problems with rust on the hubs around the sensor area...make sure they are all clean and all of the contacts in each of the plugs is clean. How did you know the sensors you replaced were bad? Did you test them?

Fulcrum525 · #3 07-04-2009, 08:06 PM

Well we definitely cleaned out the sensor area before we put the new one in.

I had the ABS diagnosed at the dealer few months ago and was told (annoyingly) that they didn't know what the exact problem was but that changing the sensor would be a good place to start.

nhdoc · #4 07-05-2009, 05:31 AM

Quote:

Originally Posted by Fulcrum525

Well we definitely cleaned out the sensor area before we put the new one in.

I had the ABS diagnosed at the dealer few months ago and was told (annoyingly) that they didn't know what the exact problem was but that changing the sensor would be a good place to start.

Did you clean the other 3? You can test them yourself with a multimeter.

Oracle12345 · #5 07-05-2009, 10:12 AM

well its most likely not the sensors and something else such as OVP etc. Buying parts for a problem that you are not 100% is causing it is stupid. Track down the problem, find out why it happened then ordered the right part.

Fulcrum525 · #6 07-06-2009, 09:20 AM

Not even the dealer knew what the exact problem was so it was recommended that I change the sensor and then go from there. Its also not 100% stupid at 254,000 miles. Once I get this fixed if it goes out again I can pretty much rule out the two front sensors as they are both brand new (And easily cleaned) OVP fuses are both intact.

babymog · #7 07-15-2009, 01:23 PM

Does it come on immediately, or when it does its ~6mph self-test?

Fulcrum525 · #8 07-15-2009, 02:06 PM

Quote:

Originally Posted by babymog

Does it come on immediately, or when it does its ~6mph self-test?

I've seen it come on immediately a few times but it mostly comes on after I've driven up to speed. (This morning for example it didn't kick on until I hit 35 mph) But it has also come on as I have backed out of the driveway and has even come on when the car is warming up in the morning.

Jeremy5848 · #9 07-15-2009, 03:00 PM

It could be the OVP but if so other things should be happening--the tach should stop working, for example.

Unfortunately, the ABS light in this model simply means that the ABS brain thinks that "something" is wrong -- with one or more of the sensors, with the pump, or with the brain itself. The sensors are at fault more often than any other component but you may have one of the exceptions.

It would be worth unplugging and replugging the big cable that attaches to the brain and checking all of the electrical connections at the pump including both ground leads (one should be a brown wire and the other a small braided strap).

One question that needs to be asked: does the ABS system still work? Can you find a piece of road that is safe for you to stomp on the brakes until they try to lock up? It would be especially good if you could do that on a wet road or a gravel road or one that has two different qualities--dry road under the left wheels, wet road under the right wheels, for example.

If the ABS system still works, the pressure to immediately repair the problem is reduced.

Jeremy

Fulcrum525 · #10 07-15-2009, 04:08 PM

Yesterday I pulled the big plug on the ABS pump itself and it was pretty clean but I wiped the contacts just to be safe. (By brain do you mean the big connector thats behind the firewall?)

Sometimes the light goes off long enough for me to do a test and yes it does work when its off. When the light is on and I do the test I just end up scrapped rubber off my tires. I'm getting a new set soon anyways cause i'm running on junk tires right no. Although that brings up a question. If one tire is more worn down then the other can that cause a system error? (I know on newer models that this is the case but i'm not sure if a 1991 model would react to the same thing)

Jeremy5848 · #11 07-15-2009, 06:08 PM

Yes, the "brain" is behind the secondary firewall.

I have heard that tire size variations can affect ABS operation. If you are truly "running on junk tires" then hold off with further work on ABS until you get four new tires all the same size.

Fulcrum525 · #12 07-15-2009, 06:31 PM

Quote:

Originally Posted by Jeremy5848

Yes, the "brain" is behind the secondary firewall.

I have heard that tire size variations can affect ABS operation. If you are truly "running on junk tires" then hold off with further work on ABS until you get four new tires all the same size.

Well they aren't so much junk as just generic low quality tires. (One of them is wearing unevenly because they went out of round fairly quickly.) Got a sent of Michelin MXV4's going on next week hopefully.

In the mean time I will try cleaning on contacts on the computer side and not the pump side.

Oracle12345 · #13 07-16-2009, 10:35 PM

any recent brake work?

another thing to think about is if your light is on then you have undervoltage problem, a current feed to the control unit interupted.

look through this-

http://www.mediafire.com/?wnulfvemdfo