ABS Light ON and Battery Dead - PeachParts Mercedes-Benz Forum

dbranc · #1 11-07-2003, 11:17 AM

Hello out there!
I have a 1988 Mercedes 560 SEL.
The problem I have is that the ABS light comes on. It does it randomly. Sometimes it comes on after starting or after driving for a while. I have checked the OVP relay and the relay located in the ABS module. The only thing I could check with the relay in the ABS module was that the diode was working. The circuit breaker on the OVP relay is good and the relay works with voltage applied to it. I have cleaned the ABS sensors on the left and right wheels. I did not check the one on the rear differential as previous post indicate that the sensor there rarely goes bad.
Recently, the battery has been discharging while the car is parked. Altenator light does not come on while driving and indicator light tests good. The car is not used a lot.
I beleive that the two problems are related. I suspect one of the relays but I am not sure. Any suggestions?

blackmercedes · #2 11-07-2003, 11:25 AM

Have you checked the alternator itself? What about the battery? In the 190E's I've owned, the "charge" light never came on to show a dying alternator, it was always an intermittant ABS light, as the ABS unit requires a certain voltage to work.

dbranc · #3 11-07-2003, 04:23 PM

Quote:

Originally posted by blackmercedes
Have you checked the alternator itself? What about the battery? In the 190E's I've owned, the "charge" light never came on to show a dying alternator, it was always an intermittant ABS light, as the ABS unit requires a certain voltage to work.

I have not tested the Altenator, I made an assumption that the "altenator Light" would come on if it was the altenator.
One follow up to the dead battery - In the fuse box located under the hood ( drivers side ) I found two relays that somehow effect the electric seat controls. These relays were very hot. I assume my battery is being drained into this circuit somehow. The car is totally off when this drain occurs, but, the relays get very hot.

blackmercedes · #4 11-07-2003, 04:35 PM

Try pulling the fuse for the seat heaters and see if that does anything.

The intermittant ABS light while driving is a classic MB symptom of a failing alternator, and many people have spent many hours pouring over their ABS system to find that it was a charging system fault. Me included.

You might have more than one problem, but it's best to rule out the things that you can right away. You might have the charging system load tested, and then you'll also have a good idea of battery health.

bill17 · #5 11-09-2003, 11:29 PM

On my 84 380SE which had same problems,

The ABS light was ixed with a new OVP relay.

The battery was also draining fast (4-7 days and it won't start) simply becuase of it's old age as it won't hold charge, which probably was made worse because it was not used frequently.

Before I got a new battery, once or twice during low battery power situations, (ie engine just barely started) the ABS light did come on intermittently, which seems to correspond to the previous posts where ABS systems needs a certain voltage to work(?).

#6 11-10-2003, 12:22 AM

ABS light will go on when bat voltage drops to 10 volts. Your car is not charging. Check brushes .

dbranc · #7 11-13-2003, 03:49 PM

I know ther in there, but, where can I get a pair without buying the complete Altenator?

G-Benz · #8 11-13-2003, 04:02 PM

Your model is old enough that the voltage regulator and brushes can be purchased seperately.

dbranc · #9 11-13-2003, 05:47 PM

Just measured the voltage on the battery with the car not running. It was exactly 12V. I then measured it running, assuming the altenator was charging the battery, and the voltage was up around 15V. I am assuming these are good readings for a charging system that works.

blackmercedes · #10 11-13-2003, 09:55 PM

If memory serves, 15V is way too high. Proper voltage is in the 13.6-13.7V range.

Regulator? Overcharging is bad too.

#11 11-14-2003, 09:20 AM

How accurate is your voltmeter? If your battery is at 12 volts with the car turned off - it is on it's last legs. A good battery should be 12.56 volts MINIMUM - 12.76-12.95 volts optimum. Just changed the battery on my wife's car - it was at 11.9 volts with the car off (car is a VW Diesel) - only found out about the battery when it got real cold overnight and the car was left outside. Went to start it in the morning and it cranked 4 times and the battery died. I charged the battery that night and let the battery sit without the charger on it overnight - the next morning the voltage was 11.9 volts - battery was toast. New battery sitting overnight has a charge of 12.93 volts on it in the morning. If your battery is truly at 12 volts - you have no reserve for your accessories with the car on and the alternator has to try and carry the full load. Have your battery load tested if it really at 12 volts - you probably have a bad cell and need a new battery. By the way - some bosch alternators will charge up to 14.7 volts with 13.9-14.2 being the norm (at about 1500-2000rpm) on all the cars I worked on. Most automatic battery chargers take the battery to 14.40 volts before shutting off or going to maintenance mode. If your alternator is charging at 15 volts at idle - your voltage regulator in the alternator is probably defective - but could be trying to compensate for a battery that is sucking the amps out of the alternator because it is unable to take a charge..