MW_ATL

Ok, I am going to guess a sensor somewhere, so lets see what the collective wisdom is - and I'll be off searching for a bit too. Here is the history:

4800 miles until an "A" service, right at 141,000 on the car over all. Front brakes have a bit over 5,000 on them, rotors, pads and sensors done then. About 7,000 on the rears, again rotors and pads, all OEM MB parts. I did the rears myself, and the fronts were done during the last service.

I do have a bit of brake squeal I haven't chased down, probably due to me skimping on the lube on the rears. I don't think any of this is going to be related, but just the history.

Car has been running great lately. Good weather and had a good spirited 80-85 mph drive on the freeway on the way home today. Everything is awesome, and then I leave about an hour ago to go to the gym. About 5 miles from the house, the BAS malfunction warning pops on. Nothing noticeable in driving, nothing eventful happened before.

I am sure I will be going to Autozone to get codes pulled tomorrow, but any guidance for now? I need to do this one myself, if I can -- and you guys know I'm one for letting my dealer handle most of these things!

Thanks!

jrsmith_68

To help you start your troubleshooting, here is a function chart of the BAS system. Check all the inputs, but as you probably know, codes will get you to the problem a lot faster.

MW_ATL

Thanks a bunch - that chart will help. I will be pulling codes tomorrow at work. I forgot we had a reader there, that will make things a bit easier.

I have noticed that it clears the malfunction, and when you turn the car back on in position 1, it stays with 0 malfunctions, but when you go to position 2, it pops the warning. I've also read on one of the CLK threads that the stop-lamp switch is frequently the culprit. I guess I have to wait on the codes tomorrow.

splinter

That’s precisely what caused/prompted the BAS malfunction warning on mine. It was an easy and inexpensive repair.

Good luck with yours.

pcy

Some cars have brake light switch installed next to the brake pedal (like on my W163 Ml320). For other MB cars, the brake light switch is integrated inside the brake booster.

MW_ATL

No ODBII Codes, which means these will only show in STAR. So now I either have to get it checked or take some guesses.

I knew I should have spend money on STAR instead of sway bars!

samaritrey

lol good luck with this and +1 On the star but sways are worth it my car drives so much better
I could be incorrect but i thought 01's had the swich on the brake pedal and then in 02 up it was ingegrated. I remember that the 01s had issues with this and someone said they rediesigned it and that this was another 01 issue. hopefully someone knows for sure.

Glyn M Ruck

It changed again at facelift. Did not mention because it does not apply.

MW_ATL

Oh yes, they are. I absolutely love it!

I played with EPC a bit today, since that was my only option. The CLK thread mentioned the switch as the problem, and Splinter had seen the same issue. The CLK thread listed A0015450109 as the part through 1999, and 2000+ using A0015453109. Neither crosses to the W203 platform, but it gave me a place to look. The W203, at least the Coupes, use A0015453809 through build dates of 07/31/2001. I checked mine by VIN and it does have this version of the switch -- mine has a build date of 05/01.

Since it is only $19.50 from www.getmercedesparts.com, I am going to swap it and see what happens. I think it is a fair gamble. We will know soon.

Gut feeling is that it will be a speed sensor on one of the wheels, instead of the switch, only because there are no problems with brake lights or the transmission shifting out of park, etc -- and I would be tempted to believe that the same switch signal would be used to regulate such things. However, considering the relative moderate price on the switch I will start there.

samaritrey

Good luck speed sensors are not cheap why can't all the parts be 19.50

Glyn M Ruck

I think you are doing the right thing. It could be a wheel sensor but get the pedal switch behind you.

Good luck!

MW_ATL

Ok, I finally got the switch in hand, and after a couple of days had time to work on it this afternoon.

The new switch:



First we have to remove the encapsulation panels under the dash. Pretty straight forward, with just 3 T20 screws along the front.



The only hard parts are removing the cable for the hood release and removing the ODBC connector. The cable for the hood release you just have to work free. The ODBC connector has two T15 screws under the cover, then you have to remove the connector from the part that screws to the panel. I did not take a picture, but there is a sliding clip on the back, you press in on the sides and slide it over and the connector comes right off.

The only other thing you have to disconnect is a CANBus connector that is mounted to the panel, then you can pull it right out.



the rectangular hole is where the CANBus connector and mounting plate go. It pops loose from the panel, but then you have to pry the connector up in the middle and slide it over to take it off of the part that attaches in the rectangular hole. if you don't take it off, you can't get everything back through that hole. You can see it better here:



The connector with all the CANBus wires (at least I'm pretty sure that is what they are (brown with red stripes and some others) sits on top of this piece and hangs out over the panel.

It got too tight to take pictures, but simply reach up the cover over the brake pedal, on the side closest to the driver and you will find the switch. You do not need to remove the cover over the brake pedal, which just has two clips and the switch holding it in place. (If you try to take the clips out, it just stays and then falls on your face when you get the switch out!!)

The switch itself is a puzzle. There is a small tab (you can see better on the picture below) -- you push this tab in, then rotate the switch 45 degrees, so that tab goes toward the drivers door and up. If twist it up and back you can feel when it locks in place.

Push the tab, twist the switch up and then *pull* and it will pop out. There is an indentation on the shaft that seems to have to be pulled loose from what ever it clips into. Then unplug the wire connector and slide the new switch in place, twist to lock in place. Everything else goes back the reverse of removal.

When I cranked the car, no horrible BAS warning light. At least for those with build dates before 07/31/01, an easy fix.

Here is a picture of the offending part. you can tell that the shaft seemed to be pushed in deeper than the replacement switch above (I wish I had taken a picture side by side!) It still clicked, but it was obvious that it had failed internally somehow.



Thanks to everyone for all their help!

pcy

The plunger you see on the brake light switch makes the contact on the copper contacts inside via a spring. Most of the times, the copper contacts wear out and the other times the spring gets lazy. The good thing is the part is relatively cheap and easy to remove as well once you learn how to 'twist-and-remove'.

Brake light switch is a well-known defect on W163.

MW_ATL

Thanks. I didn't take time to pull it apart last night to see, but it was obvious that there was a failure inside somewhere.

samaritrey

glad your car is back

johnand

I love seeing relatively inexpensive and fairly easy fixes to these cars. Glad your problem is solved.

Glyn M Ruck

Nice cheap DIY!

samaritrey

Its funny my 01 has a build date of 04/01. Funny how early the 01 was started to be built. Maybe my car is good because it was such a late 01. BTW my car had the BAS issue today but it went away so i might need your help if it comes back with the switch replacement it looks like it could be fun

rave00fever

Awesome Fix!! I had the same issue, bought a ELM327 bluetooth and also wasn't able to pull any OBD2 codes.

Also these 2 threads also indicated cruise control won't work if brake light switch is the issue
https://mbworld.org/forums/c32-amg-c...yesterday.html
http://forums.mercedesclub.org.uk/sh...ad.php?t=46128

I just took my car out for a spin and for sure I could not engage cruise control.

So I'm somewhat confident that replacing the brake light switch should solve my problem. I'm ordering the part today and will update my progress, hopefully with additional pictures.

LILBENZ230

Do the brake lights work when this switch is out on your cars?

samaritrey

Mine did work. I think the issue with mine was not that it would not go on it was stuck on. Mine has not had an issue for a week now but think I will go replace it right now for fun.
Its interesting Rave00fever you mention the cruse control years ago I had an issue with cruse working great on a long trip then i would disengage it with brakes due to traffic and sometimes would not be able to reengage wonder if that could have been the switch.

samaritrey

So mine was defective but still seemed to sort of work. It had fallen in some see pic. The worst part of this was the dam location and standing on your head to get everything out and the hood latch was such a pain to get off. Took me all of 30 or so minutes.

samaritrey

So tonight drove to a restaurant parked for 45 minutes and get in car to leave and it comes up again WTF. it only does it at night after I leave work stop after only going like 5 miles and then restart car WTF. Anyone have any ideas what to try next?

LILBENZ230

It is possible you got a defective part.. seems unlikely, but possible. I'm familiar with what BAS is, but not the schematics. I don't know what else could cause failure of it except that switch.

samaritrey

Well it could be the sensor on the brake buster or as you said a bad part. I destroyed the old one and they really don't have much in them that i would think could fail. I don't think the issue is wheel sensors or something like that because then esp and possibly abs would be acting up. The car did not have an issue today so we shall wait an see if it does not happen again i will not worry about it but if it becomes an issue often i guess i will take it in for a star appointment.