My 2000 ML 320 has 156000 miles and has been running great for over 1yr straight.

Gradually though, the brakes have softened, and now gotten to the point where the first hard push on the brakes goes nearly to the floor.

2nd push will be firm again.

BAS ESP light will go on, and stay on after any hard braking event. Turning the car off will reset the light.

I checked the Brake fluid reservoir level and found it to be a bit low. I added to the fill line. The liquid level has held at the new place, but the brakes are just as soft. No Wobble, no Squeel, but too soft, and then the light.

Any advice to diagnose or fix would be appreciated. Thanks.

 

sounds like you have a problem with one of you sensors in the braking system...there are sensors on the master cylinder on the bottom that go bad and also 3 other sensors on the brake booster itself. if the brakes feel soft you can try a really hard stop ...almost try to skid and make sure the ABS kicks in and this will ....or should build up pressure in your brakes so the pedal wont feel so soft. but your getting bas and esp lights so there is a problem with your brakes. common issues with bas esp are the brake light switch...but that will have no effect on your soft pedal though.

 

I believe if you bleed the air out of your brake system (or replace fluid as suggested in your manual) your brake pedal will be hard again. Since you are slamming the brakes now, your light is comming on because the switch see that you are compressing it too fast. There is two sets of contacts in your brake switch and if they both come on within certain time, your brake control module knows that this is emergency action but wheels sensors are signaling back that you still have too much speed in your wheels.
Could be bad brake pedal switch (it's very common problem for BAS/ESP light) but I would do the easy job first (15 minutes with another person) and see if it is better.
I'm at same milage with my ML. I will check my W163 Star manual ower the weekend for soft brake pedal.

 

Thanks for the advice.
I took her out on a quiet road, and really put the hammer down on the brake to force the ABS. Probably would have been better if the roads were wet, but I think I forced it both from Low and High Speed stops.
I was hopefull, but it didn't solve the problem. Just like pumping the break firms it up, but then after driving a bit again it softens up.

It makes sense that the sensor is actually working properly and the system is out of adjustment. (I have had several other lights over the years that were just the sensors)

I am now hopeful that bleeding the air out or replacing the break fluid will solve the problem. Not sure how to do that myself, but will search the forum for a description. If anyone knows a good link, I will read it.

Thanks so much for the advice. I have had a few problems over the years and found many solutions by searching the threads on the forum. This is the first time I have posted my own problem and I will add the outcome when it is fixed.

 

Any shop or mechanic will bleed the brake system while you wait for it, it is same for all cars. for some reason, I had soft pedal on my ML after changing my front brakes and I never removed the calipers from brake system. So I'm not sure how the air was sucked into calipers, maybe by pressing back the pistons. It took only 15 minutes of my lunch break and one coworker to do that. Lift up the front with fork lift, inserted two jack stands under and it was done in notime.

 

Thanks for all the advise. I brought the car into the shop and asked them to drain and replace the breakfluid. They said there was air, and now it was good. Brakes are firm again. $104 was a bargain to have it fixed. Thanks again.