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Old 08-25-2015, 09:52 AM
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Join Date: Dec 2008
Posts: 52
98 C280 odd ABS/ASR

Hi folks

Here's an oddity that's happened twice in the last few days:

My BAS/ASR and ABS lights came on...after some brake pulsing (on a completely dry road) so I figure that's either a sensor or brake switch, no biggie

But then inside 1 - 2 minutes the check engine comes on, which is odd. I put the OBD reader on it says there's a P0700 (transmission related) fault, which I clear. Later in the day the ABS lights go out, on their own.

The next night the whole thing replays itself, a few brake pulses and then the BAS/ASR and ABS lights come on, 60 seconds later the check engine light returns...

What would be the common problem that would activate both these seemingly unrelated warnings?


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Old 08-25-2015, 07:48 PM
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Join Date: Jan 2012
Posts: 7,534
Were the brakes pulsing when the pedal was pressed or just driving down the road not on the brakes?

If pulsing when pressed, I think a wheel speed sensor is having an issue. Sometimes metal filings, rust gets on the sensor / tone wheel making the computer think the wheel speed is lower than normal triggering the ABS.

One way to zero into this is to add a set of lights to the ABS coils and see what one is actuating or even better use a 4 channel oscilloscope and watch the wheel speed sensors.

It would be tempting to unplug any BAS sensors that are not related to ABS function and see if the problem continues. I just got a 99 C230 parts car that has 2 sensors on the brake booster ( diaphragm position and vacuum reading I think. ) and a small computer under the master cylinder.
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Old 08-26-2015, 07:57 PM
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Join Date: Dec 2008
Posts: 52
Hi and thx

When pressed. My real q is why would the CE light come on?
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Old 08-26-2015, 08:50 PM
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Join Date: Jan 2012
Posts: 7,534
I'm not sure, you need the Mercedes description of the code.

Also, Mercedes stacks grounds on a common bolt / stud. If the point corrodes, circuits start to seek ground from each other causing all sorts of odd behavior.

I have a 97 E320 parts car that exhibits left fog light on , high beam indicator on , I message on the dash I can't recall and a trans that is in limp mode. Once, all of this went away at once the the trans shifted normally. I haven't looked very hard for the problem but I bet is is a common ground opening up

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