Mysterious BAS/ETS/ABS lights don’t want to go away..
 

I just brought back my truck from the dealer after a B Service and some other major 100K tune up items last weekend.

Since getting it back, the BAS/ETS/ABS lights keep coming on (they never used to come on before – the brake switch has once been replaced a couple of years back to resolve a similar symptom).

This is what happens. In the morning at cold start they usually don’t come on for the 12 mile drive to work, but in the afternoon at lunch hour, start the truck and the lights will come on in less than 2 minutes of driving.

They will come on, on every start up for the rest of the day and the on the next day the same cycle repeats.

I already inspected the ABS relay in the fuse box, made sure the brake light bulbs are not blown, replaced the brake switch yesterday, as these are common causes of this problem. Everything seems fine. The brake lights even come on every time the brake paddle is depressed, but the mysterious lights don’t want to go off after lunch hour.

It almost seems like the afternoon temperature has something to do with the lights coming on. Only other anomaly I noticed is that as part of the B service, the brake fluid has been topped off a bit too much (way above the max. indicator)..is there something as topping off the fluid too much? Would that cause it?

Could be wrong but I can't see where a slight overfill of brake fluid would cause the lights to come on. I would however have a good look at the brake light switch which may have failed again after a couple of years. Best bet is to have the dealer diagnose it and get it right the first time. Just because the brake lights work does not indicate that the other functions of the switch are woking correctly.

I am thinking on similar lines...
 

I am going to remove the brake light switch today and re-install it.

One other thing I am suspecting about the brake light switch is the part number that I have been given by the parts dept.

A 001 545 64 09

The lady at the parts department was not very knowlegable and couldn't confirm whether this part number would work on pre-2002 models (before the face lift) or post 2002 models or both. (Maybe someone on this site can confirm)

The part number is similar but certainly different from the part number that came with the truck originally. The original part number is

A 001-545-31-09

The parts lady told me that the part number has moved up, since the brake switch has been imporved upon in the past 1-2 years.

If re-installing the switch doesn't work, I am going to take it back to the dealer and have it diagnoised properly.

sosh, I replaced the brake light switch just yesterday and that didn't help..
 

As I said, the only thing suspicious to me is the part number difference, otherwise the new switch fitted in just perfectly.

The symptoms have remained exactly the same before and after the brake switch replacement yesterday.

The brake fluid over fill is not slight - it is almost filled to the brim in the reservoir, way above the max indicator. Will post a picture tomorrow.

I can't see how reinstalling the switch will help. You are putting back the same part which could be defective. I would confirm the correct part and install a new one of those. As for the overfill, I believe but could be wrong that the only problem you would see is a leak from the overflow or vent particularly when hot and expanded. Also, have you tried resetting the steering sensors?? And, could be one of those bad also.

I confirmed with the parts dept. of another nearby dealer...
 

The part number on the brake light switch is correct. It is an updated part and is meant for 2000 (and onward) MLs...as per the other parts dept.

This means, I am just going to re-open the switch, re-install it and hope that the problem goes away. If it doesn't obviously there is some other mystery to this..

Only the dealer might be able to tell...

Based on my experience with these lights, there are 4 causes. The common one is the brake switch. In this case the lights just come on (I don't recall what sequence of lights come on though) and after replacing the switch they go away - happened on my E430. The second case is related to steering angle sensor - Code C1174 I believe. The third case happened on my 02 ML320 - ESP/ABS/BAS and ETS all came on. Diagnosed to faulty ESP control module. The last case will lock up the shifter - In my case it was BAS/ABS and Pad Wear lights that came on. After restarting the truck, I was able to shift. This was diagnosed to a faulty ESP/BAS control unit (Code C1000). It turned out that in this case, my alarm did not do the three blinks anymore. I don't think that was related to the BAS/ETS/ABS thing though. But that one was diagnosed to a faulty trip computer - Code B1716. If you don't fall anywhere within these categories, then there's possibly a fifth reason foe these things to go bad. I'd say, have it diagnosed by MB and then based on the codes that are read, they'll tell you what needs to be replaced. From there, DIY or have them do it.

BTW, none of these affects your braking or sliding performance though!!!

Attached are the images of the fluid top off after the B Service
 

Darkmann, firstly thanks for the informative post. The light on my trip computer has blown for quite some time, and the shifter bushings are worn out (one of them is even misssing - probably fell off after so much wear), so both are likely candidates.

My truck was in last weekend for the 100K tune up and part of it I had ordered the tranny service (now that you talk of the shifter related in some way to these lights, would the tranny service have altered something to cause the BAS/ABS etc. lights come on?). They flushed all the tranny, transfer case and differentials, and left a note saying the shifter bushings were worn out. I just think, they should have gone ahead and replaced the bushings...I was paying a full $600 just for the tranny service anyways..and even if replacing the bushings ($1.50 a piece) meant another half an hour or so of labor (I am told they are very easy to do, once the truck is lifted up), I wouldn't have minded paying it. I have already booked another appointment for this Saturday and will be taking the truck in for the shifter bushings and these lights coming on.

From my side, I re-did and re-checked the new brake switch's wiring and setting...it seems fine...the ABS/ETS/ESP lights are still come on.

I am taking it to the dealer for diagnosis this Saturday and will post the outcome.

Attached are the images of the fluid top off by the dealership at the B service..way too much fluid in the reservoir...one other thought racing my mind is, although unlikely, what if they topped it off with the wrong grade of fluid?

Have you tried what I mentioned re resetting the steering angle sensors by turning full one way and then full the other??

I believe the brake light switch is more complex than it appears, it can still be faulty even if the brake lights work normally; there are two sets of contacts which are both used for initiating the BAS system.

Whilst putting extra foam sound insulation round my footwell I inadvertently interfered with the brake switch and had strange symptoms - seeming as if the BAS was continuously, but partially, engaged. Needless to say I removed the extra foam promptly.

Yes, I tried that yesterday evening..
 

I re-did the brake switch, tried resetting the steering angle sensor, by turning it both ways holding it for 30+ seconds each way.

The light hasn't come on today morning (routine behavior) I will only know at lunch hour (that's when it comes on) whether all I did yesterday made any difference.

I am more concerned about the fluid top off too, since the lights come on only around noon (temperature related - too much topped off fluid - fluid expands due to heat - builds up unusual pressure in the circuit - BAS/ETS/ABS lights come on)

All in all, it is going to the dealer tomorrow anyways for the tranny shifter bushings..if the lights keeps popping up, I will have them look at that too..

Lights came back on at lunch hour...
 

Less than a minute into the drive at lunch hour, the lights came back on. This has certainly something to do with the temprature. I am more and more suspecting the brake fluid now, since fluids are the most sensitive to temprature changes.

It certainly has to go the dealer tomorrow for this. I'll know what it is then...I will post the outcome.

Got the issue resolved finally...
 

Took it to the dealer this morning and they could solve it...I informed the mechanic of all I had done to solve the problem.

The brake switch, The relay, resetting the steering angle sensor etc.

My mechanic talked to me about it all and then hooked up the truck to the STAR diagnostics computer

The following codes had registered on the computer
C1200, C1401, C1140, C1141

I couldn't catch what all those meant, but I remember at least 3 of them.

One had to do with the brake light switch (might have registered when I replaced the switch)
Another had to do with the ABS pump
Third had to do with brake pressure sensor
and I don't remember the 4th.

Of all he code C1401 (ABS pump) had registered itself 11 times in the last week, and so that concerned him the most.

He cleared all the codes and took it for a test drive. Only the C1401 came back of all. His initial inference was the ABS pump might have gone bad. He ran some electrical tests on it and nailed it down to the relay.

Since I had already told him about my having replaced the relay, he was a bit surprised and so was I, until we both took a closer look at what relays we were talking about.

There are 2 brake circuit related relays in the fuse box. One is for the brake light switch (K12) and the other is for the ABS pump (K25).

I had replaced the brake light switch relay (K12), but not the ABS pump one, so that's what it was.

He checked my service history and told me, I haven't had a brake flush in 3 years, so we decided to have that done too..

The truck is back, and my mechanic was confident, the lights won't come on again...if they did, I should just bring it in again..

Thank you for the detailed report! It's the first K25 ABS relay failure I'm aware of.

Pictures of the relay..
 

My mechanic even dissected the K25 relay to confirm..

After seeing this, I am convinced, he has indeed nailed it right..the lights won't come on anymore...

The temperature dependence that I was seeing might be related to the ABS hydraulic pump having to work harder (draw more current) in warmer temperatures...causing the code to register each time in the noon..

Here's another idea. There are several of these same relays in the E-Box. For testing purposes one could remove one of the others and exchange it with the one suspected to be faulty. Here's a picture of the E-Box, with six of these relays, all in black, in a 1999 ML320.

When the ABS malfunction light flickers it's usually a voltage supply problem, of less than 10.5 Volts or so. In your case probably caused by excessive ABS pump relay contact resistance...

http://www.whnet.com/4x4/pix/fusebox.jpg

I used the same technique that you have mentioned below....
 

to resolve another mysterious & nagging problem. There were at least 2 people on this forum who had reported and discussed this symptom with me almost a year back & we were all clueless as to what would cause this...

The wipers die intermittently while driving in heavy rain or extreme cold weather......this problem has been nagging me for the past 2 years and is as mysterious as those BAS/ESP lights were....

The only explanation that we had at that time is a bad wiper motor or its wiring gone bad...

While working on the BAS/ESP relay, I noticed, the wipers too are swept by a relay. I decided to swap the central locking relay with the wiper relay just to see if that would give any clue. At first, nothing changed, but a month later, the central locking had its first hic up on an early morning cold start. The lights blinked once on OPEN, but the locks would not flick..a couple of lock - unlock attempts solved the problem. Then a few days later, the same symptom reappeared.

Today was the third time in the last 2 months, that I had the symptom reappear. This time around though it was bad, the locks completely stopped moving. Nothing would help. I promptly swaped the central locking relay again with the wiper relay and sure enough, the locks are back up, and wipers are completely dead now...

Failing K17 relay is what it was all the time...I bet...

I just need to wait for the labor day weekend to be over here, and run to the dealership and pick up a replacement relay, and I probably won't see that wiper problem ever again at least for the next 2-3 winters..

You use your wipers??? It's been so dry here lately that
 

I probably have forgotten where the wiper button is. All kidding aside, I hope that relay fixes it for you.

Those wipers bothered me like hell last winter..
 

By the time winter was almost over (April), the wiper problem had drove me nuts with no one on 2-3 forums having a clue of what exactly could be the cause...

I happened to accidently discover in the same month that the wipers were swept by a relay. So, I swaped my central locking relay with the wiper relay. For about 2 - 3 months the central locking kept working fine on the wiper relay (central locking would tax a relay far less than wiper sweeps, that explains why a partially bad wiper relay kept central locking working for so long)....but after that the hic ups started with the central locking too...

I am so glad, I nailed the relay down before the onset of this coming winter. It is not fun driving in heavy rain/snow with the wipers deciding not to work on their own whims.

Neither the wiper motor nor its wiring would have been an inexpensive fix, plus taking it to the dealer and having them spend hours on diagnosis would have been expensive too. Such a problem is extremely hard to diagnose, since the wipers would only die intermittently in extreme cold weather. To diagnose it right, the right conditions would have to prevail, and the wipers would need to stop working for anyone to run some tests and nail down the problem.

After all a cheap $20 relay is all what was the source of it all....but it did take me 4 months to nail it down...

I took mine to the dealer a couple of weeks ago for this BAS/ESP light and they said it was the steering angle sensor. Its like $300 plus 5 hrs labor... So needless to say, its still on.

So, your going to continue to drive the vehicle with one of the most important safety systems inoperative??? That is irresposible and hazzardous to not only you but others on the road. When you are finished with the vehicle how are you going to explain to prospective buyers why this is inoperative?? Be smart, spend the bucks and get it fixed correctly.

I had my 3 little lights coming on & off for a year now. did all the "DIY" thing that is, replace the brake switch, replace the relays and so on... but no luck. Tired of seeing that 3 little lights went to the dealer to have it diagnosed - BAM - BAM the culprit --- ABS pump. and the sad thing is that I got no more warranty. So far until now my ML runs sooooo gooood.

Excuse me, but who the hell are you?? So the traction control is out, big deal... There are thousands of vehicles on the road that don't even have that option. My bad that you need it in order to drive but some people have real driving skills and don't need all those fancy options, its nice, and it will be fix in the future, but to spend $1600 because some random light comes on and off at will is a little much. I know the limits of my car and when its wet or the conditions aren't the best I watch how I drive. I mean its an SUV anyways so I dont push it like a car. If your scared of me driving on the road with you, then stay at home. I guarantee my BAS/ESP light going on and off is the least of your concerns.

Why are MBs so expensive to fix??
 

It almost feels like such astronomical repair costs simply defeat any justification to holding on to a MB after 5-6 years...If repairs are so expensive, why doesn't MB build stuff that really lasts long??? At least critical components like the steering angle sensor, ABS pump etc. etc.

The steering angle sensor & ABS pump going bad are both expensive fixes. That's what I kept praying all week while I waited to be attended by the dealer. The last thing I wanted was a replacement on any of those..

Fortunately in my case, it turned out to be the ABS pump relay ($20)....so I walked of those lights this time...

I just read somone on this forum looking for the front differential...another vital component. Why do these have to start failing???

Just came back from the dealer and it turns our to be $2500 repair - control unit needs to be replaced. $1700 part. Not sure what to do.