Hi; I need some help. I have been searching the forums but I don't quite seem to find a similar problem.

Car: ML350 2006, 160K km

It all started with what I thought was a failing battery. So I replaced it. The below listed symptoms would happen before, and sadly after the battery was replaced.

PROBLEM 1.1

It started with my ABS light coming on.
ABS unavailable message, ABS light on.
Orange triangle with exclamation mark on.
EBS unavailable msg.
Flat tire indicator inoperable msg.
Cruise control not functioning.

I took it to the Benz dealer, and they replaced a couple 'cards'.. they look like small mother boards for a computer. Anyways... one controlled the lights and was in the trunk, and the other one... I have no idea.

When I asked them to look at the ABS and tell me whats wrong, they said they could not pin point the problem, but they said it was either the ABS Speed sensor, which they said they cleaned, or if not, something to do with the axle - either way, they told me the problem seems to be gone after they cleaned the ABS Speed sensor, and that I should no have any major problems.

1 week later, I went on a road trip, and each time I got in the car, the amber triangle and ABS lights would come on at exactly 35 km/h. About 1000 km into the journey the lights just stopped. The car worked perfect; I thought well.. maybe it sorted itself out. i WAS WRONG.

PROBLEM 1.2

When i took off from a gas station, my car all of a sudden engaged the ABS involuntarily. My foot was nowhere near the brake pedal. As a matter a fact I was pressing the gas pedal but it seemed like the car was stuck in first gear and would not gear up... and so I could not accelerate. At that time when the ABS kicked in, I could hear a grinding noise as if I drove over a tall and icy snowbank. This kept happening until i got back to the gas station. I turned the car off, I started it again, the orange triangle, and ABS lights came on and messages. I was ****ting my pants considering I had no shoulder to pull off onto, and another 3000 km to go. I decided to keep driving. 300 km later I pulled over and turned the car off. When I got back in the car it was like the car was perfect again. No warning lights, no messages, no warning signals.

When I was visiting my family, I found a BMW licensed mechanic/technician that offered house calls. He came down to see my at my folks place, and as soon as I told him the problem he said he knows what the problem is: the abs control module. He said there is no messages in the system, as if there was no problems with the car. I told him the story as above; and he said that it had to be the ABS module. He mentioned his computer could not communicate with the ABS module and he said that is why the ABS engaged, and I lost power, because the ABS control unit would disallow the car to accelerate as it engages the ABS.

I am going to have this module changed out by him (at a much cheaper rate then benz) but just in case it does not work, I wanted the communities input on this. If it does get resolved, I will follow up on this post and tell you IF the problem got solved.

 

I have seen similar problems on other manufacturers all because of a faulty wheel speed sensor. I currently have a vehicle with this problem. Every so often the traction control will kick in for no reason and occasionally pulse the brakes when stopping. I believe it is one of the front sensors for me because it seems to be more common when turning. Once the system goes completely offline it should store a code telling you which speed sensor is having trouble. Unfortunately until it goes completely inoperative it won't set the code. I believe it will also reset on each key cycle. It needs to fail completely before it will be easy to diagnose.

 

I have the same problem with my 2008 ML350. It started after I got the front tires replaced. It is strange because it happens more right after I fill up the gas tank (maybe having something to do with the weight distribution in the car?). I will head onto the freeway and as I accelerate the triangle will start to flash and the car will not accelerate any more till I let off the gas and give it a second or two. Then I can slowly start to accelerate again and it may or may not happen again. Sometimes it can happen for five minutes or more. But, I can always make it stop by getting off the freeway and coming to a complete stop (at a light for instance). Once I do that it will not reoccur till I turn off the ignition and wait a while. Has me and my mechanic stumped.

 

...unfortunately it has plagued me three times, I've had 3 of the four wheel sensors go in the last year, which makes me wonder if it is a manufacturing fault. Although it is relatively easy to fix, it can leave you in a real bind when the car decelerates into crawl mode (in one case, a foggy motorway with no shoulder, in another, going through a set of lights).

Thankfully our local MB dealer/servicer has done a fantastic job of finding and fixing the problem (after a few false starts with a cheaper analytics garage).

 

It does sound like a wheel speed sensor - it fits all the symptoms you describe. They are cheap and easy to fix. They are also very easy to break because of their location.

 

I had to replace all 4 wheel sensors over a 6 month period one at a time, each time one was replaced the car would be fine for a month or so then the ABS light would come on again.

I am lucky enough to have a top end diagnostic reader that allows me to bring up each wheel on live data to double check the fault codes, thought we were just very unlucky, but there seems to be a trend here with the sensors.

 

Hello ! From what I read, I had a similar problem with the ABS / ESP and diagnostics showed me "the power of high-pressure pump." The problem was the electric motor of the ABS pump or in particular carbon brushes are worn and occasionally make contact and then not make contact and therefore does not lights

constantly but only occasionally.