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?

Thanks

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.

Hi and thx

When pressed. My real q is why would the CE light come on?

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