....another ABS, BAS Light question.....? - PeachParts Mercedes-Benz Forum

prevost3000 · #1 06-30-2006, 02:01 PM

1998 Mercedes S420 has a warning light problem.

When the key is turned on all warning lights illuminate, then after startup, 2 lights remain - ABS, BAS/ASR. They stay on solid even before the car is moved. They never go off at all, and have this problem for 3 months solid.

THings I have checked:

Battery voltage - 12.6 off, 13.96 running constant, batt looks great and is white merc battery.

Fuses underneath black cover at PAX side of eng compartment, there are 3 - red, yellow, blue. All good, no corrosion, has 13.9VDC while engine running.
Brake light switch operation - when the pedal is pressed, all 3 brake lights come on, then go out after released. Lights do not stay on due to a faulty brake light switch, and then bring the batt down.

Please note that the brake lining light is not on and nor is the red brake light warning against brake fluid level.

I have not reset the neg connection at the battery, but I did unplug all 3 computer modules under that black cover in the eng compt. When i reset them, the lights did not change behavior.

Question? The black thing that the fuses plugged into, was it the ABS module? I kinda thought it was the skinny black one next to it. I could not get the one with the fuses out (and who knows it may not come out)

I have learned all i can from the past forum searches, now I need to create application specific assistance. Please chime in and lets stay on topic.
Prevost3000

Carlos Serrano · #2 06-30-2006, 03:13 PM

Just for the hell of it get in your car turn it on and turn your steering wheel all the way to the left till it stops and hold it there for 5 seconds, then turn the steering wheel all the way to the right till it stops and hold it there for another 5 seconds and let us know what happens. This is a syncronization process for a 1999 SL 500 ASR BAS system it may be worth a try.

prevost3000 · #3 06-30-2006, 03:50 PM

i started it, and the lights remained on.

I cranked the wheel left and held against the stop for a count to 5 (i heard the press regulator hiss from the steering system) then i cranked the wheel right and held against stop for 5 seconds.

The lights never even flickered. I then tried it again in drive stopped. nothing.

Lets try something else.

BTW the manual says that if there is an ABS code, the BAS/ASR light accompanies this problem. I think there is nothing wrong with the bas system, its just on for the abs problem.

How do i pull the error codes from the abs? I went to autozone, they could only do the engine.

Help.

shandy · #4 06-30-2006, 04:19 PM

Change your brake light switch, this is the most common cause of ABS/BAS/ASR light remaining on.
Even though the brake light system is operating there is another circuit which shares this switch and causes the warning lights to remain on. Cheap and easy to change once you get to it.
Geo.

prevost3000 · #5 06-30-2006, 09:19 PM

Ok. Final update.

The car is fixed.

Let me tell you how. THanks to Shandy. I went to ParkPlace Mercedes and bought the switch for $31 incl. tax.

I replaced the switch on faith and did not test the old one. I turned the key on and started it and the lights immediately went out. Hooray!!

Thanks Shandy

I thought that the brake light switch drained the battery and caused the battery to fall below the threshold and cause the error.

The switch has 2 2pin plugs on it and perhaps its a redundancy built in or not. I dont know. but it worked.

Prevost

92497pmu · #6 07-21-2006, 03:58 PM

Is this the brake light switch under the dash (@ the pedal) I assume?

Thanks in advance
PMU

Jakob F Prasz · #7 02-28-2008, 06:00 PM

Change the brakelight switch. The Switch is part of the CAN bus for the BAS. Does you crousecontrol work? if not, there is doubt, the brakelightswitch :-)

CAZUMI98 · #8 03-21-2008, 10:50 PM

I own a 2000 C230 Kompressor. I have the same problem. I have replaced the switch 2 weeks ago and the lights went away. That is until this past monday. Now they are constantly on. Cruse control works but at times the trans goes into limp mode. I have to re-start the car and all is well with the exception of the lights. Battery is fine alternator is fine grounds are fine. So, is there a posibility that the new switch may have gone bad that quick? Should I try another one? Any sugestions would be apreciated.

Mike V.

david s poole · #9 03-22-2008, 12:13 PM

where did you buy the switch from?

CAZUMI98 · #10 03-24-2008, 10:35 PM

Mr. Poole,
I got the switch from the local MB dealer. I must say that it did not look like the one I took out (Cheap). Should I try another one?

Mike V.

david s poole · #11 03-25-2008, 10:36 AM

from your description yes you should.that brake light switch has to let the other computers know when you take your foot OFF the brake otherwise conflicting info sends the system into convulsions.

fastfestus · #12 04-01-2008, 04:04 AM

Hmmm... I might try all this tricks tomorrow to see if I can get rid of that "Always On" ABS warning light. Meanwhile, I'll keep reading other's solutions.