SLK (170) BAS/ESP Light

[K-T]

This is my first post, it sounds like something which has been done to death but stay with me, it's different!

I have a manual 170, facelift late 2002 special edition.

My BAS/ESP and blown bulb lights come on when I start the engine, more accurately the blown bulb light comes on straight away after engine start and the BAS/ESP light comes on the first time I apply the brake and it stays on. This results in the brake lights not working which is a little upsetting. When plugged into STAR it registers fault code c1200 - brake light switch implausibility where half of the switch works and the other half doesn't. So, we change the switch and all is well, for 2-14 days that is, until it does exactly the same thing again. After three switch changes I pulled it myself, reset the switch actuator length and plugged it back in and hey presto, it works again.

So it's not the switch that's doing it, or reinstalling the old one wouldn't fix the problem. The thinking from my local merc specialist is that removing the switch 'reboots' a controller which then gets its act together. MB parts dept looked at me blankly and told me they'd never heard of brake light switches failing and offered to sell me a fourth one, I told them where they could stick it There was lots of clucking and 'that's terrible' coming from them, what a useful bunch of people, NOT.

As an aside I found my passenger footwell to be full of water last week and dried it out, one solitary leaf had blocked MB's excellent windscreen drainage system, not sure if this is linked.

Anyone have any ideas about where the problem lies? Sometimes it fixes itself just on restarting the car, my thoughts are that the unit which receives data from the switch is knackered, does anyone know which unit this would be? Or indeed whether anyone else has had this same problem and found the culprit?

All ideas welcomed, this strikes me as being an expensive fix :-| At present I'm not exactly loving my recent transition from Japanese to German cars, I love the whole idea of the car but since Merc in general appear to be either a source of expensive technical problems (this switch thing) and cr@p design (the windscreen drainage) I suspect if it's not fixed in the next few weeks then it'll be out on its ear, it's just a shame no-one else does the 2 seater hard top roadster so well

Thanks in advance for any assistance

 

[television]

I want to think about this for a bit, I will post back

 

[Uncle Benz]

Could be a long shot, but pull out the brake light bulb holders and check the contacts are not burned. I have seen a couple where the holders and the lamp units themselves have been quite badly burned out.

 

[K-T]

I've tried the brake light bulb holders extensively; I've changed bulbs, swapped bulbs and tried unscrewing them *just a bit* in case the contact is broken, all while the fault is present but to no avail. Reading on here it sounds like the problem would be evident, ie arcing and melting, however there's none of that on the holders or as much of the receiving slot that's visible.

When the switch kept failing but was fixed by the replacement it was always (for me, not MB) a question of whether it was the switch or the interference with the system that was fixing it, now I think I've conclusively proved it's the latter, however I have no idea which part is being affected! The specialist wants a morning to troubleshoot all the wiring to make sure there isn't a short in there, and failing any joy there he's talking about changing the ESP control unit, which sounds expensive. The problem is that even if I can get it to him in the failed condition to test (very dangerous, driving across bristol with no brake lights) there's still no guarantee it'll still be failed when it gets there and as soon as the switch gets pulled it fixes itself!

Thanks for any help

 

[K-T]

No-one have any ideas? It's going back to the specialist tomorrow as the light came back on today and I don't like the idea of resetting it myself every week. He now thinks it means the ESP unit needs changing which sounds expensive, if anyone has heard of this before then this is the moment to speak! ESP is definitely working normally as it got upset when I got the back out a little too much for it this morning ;-)

There's no change in the problem, just random occurence still with loss of brake lights and resets on disconnect/reconnect of the brake light switch.