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-   -   ABS brake light (http://www.peachparts.com/shopforum/tech-help/7164-abs-brake-light.html)

fz500sel 04-16-2000 11:34 AM

Coupla' days ago, while drivin' my '84 500SEL (Euro) the ABS brake light came on. The brakes felt fine and the car would brake okay. I checked the brake fluid level and it was at max level. Since then the light never came back on......until just now.

What could be the problem? Any help would be appreciated.

Brain kicked in and I did the ol' archive search for this problem. Seems like I may have a bad sensor according to all the previous posts. Is this an easy thing to check? I'm a moderate DIYer but am willing and eager to learn more.

Thanks,
Frank

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FrankieZ
84 500SEL EURO 87K
85 300D 267K (and still goin' strong)

[This message has been edited by fz500sel (edited 04-16-2000).]

[This message has been edited by fz500sel (edited 04-16-2000).]

stevebfl 04-16-2000 08:49 PM

You surely have a sensor problem.

Diagnosing which one isn't so easy. Your sensors are working most of the time or you would be getting the light all the time. Because the car wheels travel at different speeds when cornering or going over bumps the controller has to decide the difference between such activity and poor signals.

We use the Bosch tester and when used according to design these problems couldn't be decided. Bosch and MB say to test each sensor by turning the wheel while on the lift. For years we never found the sensors using this method. Finally we tried driving the car at 2-3 mph (holding constant speed) while switching from sensor to sensor. By doing this one can see the differences. Doing one wheel at a time the differences in wheel speed caused greater differences than the problems did.

These tests could be done with a voltmeter and/or scope. But the problem will be switching from one to the other for comparison under similar circumstances.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

fz500sel 04-16-2000 11:10 PM

Thanks, Steve.

Sounds like I should take it to my German mechanic. He is a Bosch service tech. How much can I figure that a new sensor will cost?

Thanks,
Frank

------------------
FrankieZ
84 500SEL EURO 87K
85 300D 267K (and still goin' strong)

mbdoc 04-17-2000 09:33 PM

Remember that if the light never goes out after starting, then there is a voltage supply problem.
If the light comes on while driving & goes back out when starting then the problem is a sensor.
The charging system also is important to system operation.

------------------
MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V

fz500sel 04-19-2000 09:42 AM

Thanks, Steve and MB doc!

It sounds definitely like a sensor cuz it will not stay on when I first fire up the car but will come on after about 20 minutes of driving. How much do you figure a new sensor will cost? also is it dangerous to drive like it is or can I wait awhile?

Thanks,
Frank

------------------
FrankieZ
84 500SEL EURO 87K
85 300D 267K (and still goin' strong)

stevebfl 04-19-2000 11:53 AM

The front sensors are $156 and the rear is $118 MB list prices. They should be available for a little less.

We seem to get more right front than left fronts and the fronts in general more often than the rear.

You might try cleaning the fronts if you can get them out without destroying them. They are magnetic and can accumulate metal from the brakes.

When the light is on the ABS is inactive. The brakes should work as well as any US 500SEL without ABS. In other words the hydraulic brakes should be normal.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by stevebfl (edited 04-19-2000).]


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