ABS Light came on, later was off - PeachParts Mercedes-Benz Forum

jbach36 · #1 09-15-2006, 02:31 AM

Just over the last few weeks, my brakes have been squealing. I took the car into a shop, they looked at my brakes, with wheels on, through the hub view. They can see the rotors have the normal Mercedes problem (yet another one of their problems) of having a ridge around the outside of the rotors, where the pads don't hit the rotor. He said the pads have plenty wear left on them, the squeal is yet another gift from Mercedes; they and Volvo are the leaders in brake squeal as he tells it. The back brakes haven't been checked yet.

Today I was driving along, and the ABS light came on. Scared the crap out of me, as I think stopping is a wonderful thing. I kept driving as I was late for an appointment, and couldn't get off the road anyways. After my appointment, I looked through my manual, and was pleased to read that if the ABS light comes on, the brakes work normally, just the ABS is out. The ABS light came on when the key was turned on, as it was supposed to. When I restarted the car, no ABS light was on, as it normally should, and it hasn't come back on since, as though all is well. I'm guessing whatever problem it had while driving, it reset itself upon startup. Anyone know about what the problem might be? Maybe it was a one-time thing.

Thanks,

Jeff
1991 300d, 93k

wbain5280 · #2 09-15-2006, 05:31 AM

Typically, the metal pieces in the brake pads get into the reluctor wheel and sensors. To fix this issue, you will have to take the wheel, caliper and hub/rotor off to clean the reluctor wheel. You can then clean the metal bits from the sensor, which goes in from the back side of the spindle.

The fact that the ABS light comes on means the ABS has a fault that needs to be checked, but you still have brakes.

jbach36 · #3 09-20-2006, 12:01 AM

Did you mean in the front or rear brakes?

jeff

david s poole · #4 09-20-2006, 09:48 AM

he means front,your car should only have one abs sensor in rear in diff housing.now to squeeling brakes.this symptom usually occurs at low speed as you are almost stopped.it has nothing to do with the wear lip on edge of rotor.it is caused by interaction between the caliper piston and the brake backing plate.if you know a good tech have them take one or two pads out of the calipers [front and rear] and when you look at the piston side you will see nice shiny imprints on the metal.solution.......fit shims behind all brake pads or buy good quality pads such as textar which have special padding built into the backing pads.your car being a 124 car your front brakes are floating caliper and not so prone to the above so start with the rear brakes.

Gilly · #5 09-20-2006, 05:48 PM

OK, ABS light: Ccould be the OVP (overvoltage protection relay) or another common problem is a wheel speed sensor, the wires get open circuits especially on the front due to the wheels turning left/right. May be codes in this car or just have to do a test of the whole system, not sure on a '91.

Squeeling noises, can be fixed, lots of shops just like to say "it's a MB, what do you expect?", but this is a cop-out. Important things are to clean the slide area when replacing pads and thin film of grease where the metal backing plate of the pads contact the caliper, and I just used a thin coat of grease on the back of the plate also where the caliper piston contacts the plate. Next, VERY important to bed in the pads properly after replacement, either with new or old rotors (don't machine the rotors, reuse is fine usually just once, but don't machine them). Need to do a series of very hard stops, if you have ABS you don't want the ABS to activate, but JUST above that threshold. Do that about 5 to 10 times, maybe 30 seconds or so between brake applications so's not to get the brakes too stinkin' hot. THIS helps keep the brakes from squeeling. If you don't the pads can glaze and they never really do get bedded very well. Don't know why, it always worked for me though. If you are reusing the rotors be careful as the first few stops will be pretty lousy until the pads get the groove cut into them from the lip on the rotor. I think every car gets that lip on the edge, not just MB.
Gilly

Larry Delor · #6 09-20-2006, 05:50 PM

I'd like to add that metallic pads can cause sqealing, as can accumulated dust. Use OEM pads, wash your wheels when you wash your car.
The ABS light can also come on if your brakelight switch is getting alzheimers. Just keep an eye on it...if it keeps happening, get the code checked and fix it.

As far as that ridge goes, I've had that happen on non-MB's too, so don't call it a gift from MB, but rather from the those that designed the brakes.

Gilly · #7 09-20-2006, 05:59 PM

I just don't think the ridge is really an issue, doesn't harm anything. Bothersome yes, but inherent to the design. Good point on the pads Larry, choose your pads wisely. Worry more about how well the car stops and less on wheel dust, IMHO. Yes the harder pads are more prone to squeeling and I don't think the cars stopping distance is improved, probably worse, but less dust and last longer. You'll have less dust and longer lasting brakes if you toss a boat anchor out the window, but that ain't really stopping you better, is it.....

Oh I should point out if the ABS light came on while making a significant turn (say at an intersection or turning a corner in a parking lot, etc, more than say 1/2 a turn of the steering wheel), then quite likely it's a bad wire in a front wheel speed sensor.

Gilly