Hello all, after browsing various threads on here and other mercedes forums there are a lot of posts with similar symptoms to mine but not exactly the same.

Approx. 2 weeks back I parked my car up at work as usual, then roughly 9-10 hours later returned to the car to drive home. Switching on the ignition I got the ABS/ESP/BAS inoperative come up (the BAS fault disappears after starting), so I switched off and on a few times to see if it would clear. No luck. On my way home I pull in to my usual mechanic as he has a snapon diagnostic machine, plug it in and sure enough the brake light switch comes up. Now the mechanic is very busy so I book the car in to see him the following week, he has changed the brake light switch to a known working one and reset the codes however the code comes back and the faults remain on the dash, all relevant fuses etc have been checked and confirmed okay. With my limited understanding I believe he has chased a signal to various parts of the car but unable to get a signal at the individual brakes. Interestingly on a test drive he has told me the ABS does in fact work as it should.

The mechanic who has the car currently thinks this could be a faulty ESP module, or perhaps chafed wires?

A shorter chain of events is as follows..
Wash car at weekend with home jetwash (including wheels but NOT the engine bay)
Drive to and from work happily Monday to wednesday, drive to work Thursday morning, symptoms start Thursday afternoon.
Take car to garage, snapon diagnosis says brake light switch and a few under voltages)
Friday i test the aux battery with multimeter (reads 12.5 with engine off)
Drive car for a week with the faults, traction control confirmed definitely not working.
Drop car off on Monday, garage replaced brake light switch, doesn't fix the issue, checks fuses etc, all okay. Spends X amount of time during the week investigating but nothing has jumped out at him to say it is definitely that.

As much as I love cycling to the gym and work at 6 in the morning, completing a full day at work and then cycling up a gigantic hill to get home, I really would love to get a but closer to solving this mystery.. so..

Has anyone here had this happen to them as well? Does anyone have some inspiration to offer on what this might be? Or am I better taking this to a dedicated mercedes specialist in the hope they will have a solution?

hopefully you guys will have some thought I can discuss with the mechanic

Thank you in advance and sorry for the long post!

 

Battery testing with a multimeter does not indicate battery condition. At 4 years old, it is time to consider replacing the main and aux batteries, just because. Batteries are wear-tear items and don't last forever.

What codes are being stored? You need more information.

There was a recent post on this site with similar symptoms (you didn't post codes however) and it turned out to be a wheel speed sensor.

Check the obvious things first. If the brake pedal sensor didn't solve it, then keep going. Replace the batteries and read the codes after the batteries are replaced.

 

Hello chassis, thank you for your reply.

I am going to the garage on Monday after work so I will ask what codes remain after they have been reset, I will then update this post with he extra info.

I have mentioned the batteries before to the mechanic, but will mention them again whilst there. As you say they do have a life expectancy and as far as I'm aware they are still the original batteries, I do also do a lot of small journeys so this is one of the first points I had considered before dropping the car off at the garage.

Do you suggest buying the batteries from mercedes or are there a list of known, suitable replacements?

Thank you again!

 

I would buy the batteries from the dealer, unless they are significantly higher priced than other retail outlets. Here in the US the car dealers seem to charge not-too-high premiums for batteries.

 

Quick question. Is the mechanic you took your car to someone who works on German cars, specifically MB vehicles, regularly or is this more the local garage / gas station? The reason I ask is the first thing most indy MB or BMW specialty shops do is hook up the car to the diagnostic systems for the specific brand of vehicle and take a look at all the fault codes captured by the vehicles logging system. They also have diagnostic routines that they can run on the vehicle to help narrow down the root cause of a problem. From what you're describing so far, it seems the right diagnostic tools may not be what are being used.

Unfortunately, the days of using a multi-meter and generic tools to troubleshoot most vehicles, especially the higher end cars, is long over. What we drive today are essentially computers with wheels and a steering wheel. The result is the kind of performance and reliabilty cars from just a few decades ago could never achieve. The computer systems in our vehicles run everything and are all inter-connected through dozens of monitoring / control modules. So you really need to be using the correct diagnostic tools to get to the root cause of the problem. Otherwise, you could end up going through a very costly trial and error process in trying to find the root cause of your vehicle's problem.

 

Hi Paul, you are quite right. This is a mechanic who works on a lot of cars for people who work at the company I work for and comes very well trusted and recommended.

Although like you say, he does not solely work on German or mercedes cars. He uses a snapon device not the STAR system that a mercedes specialist would use, so although it does seem to be interfacing with the vehicle, perhaps it is not pulling all the information a STAR device would be able to.

He has given me the option of taking it to a local indy instead and so I think this might be what I do.

 

For those interested - the fault was found to be within the wiring of the ESP module, the fault was not being picked up by the original mechanics diagnostics systems but the STAR system obviously picked this up.

Drove the car for a week and now I have engine management light, will start a new post for advice as it is an interesting one!

 

Thanks for the follow-up reply on the problem resolution.