Hi all,
I’ve been chasing an intermittent electrical fault on my SLK for a while now and I’m running out of ideas.
The issue is this: I sometimes get both the bulb failure warning and the BAS/ESP warning light at the same time, and when that happens, the brake lights stop working completely.
The fault is totally intermittent. It comes and goes randomly, with no clear pattern or trigger.
So far, I’ve already had the following replaced:
Brake light switch / brake pedal switch
The two relays related to that circuit
All parts were genuine Mercedes-Benz, and the work was done at an official MB workshop.
Unfortunately, the problem still comes back every now and then.
Has anyone dealt with something similar or got any ideas what else could cause this?
A bit more detail:
Yesterday the warnings came back on again, and as expected, the cruise control also stopped working.
Then I switched the engine off and restarted the car:
first it showed only the bulb warning
then after another restart it showed only the BAS/ESP warning
I also tried pressing the ESP button, but nothing happened at all — it was almost as if the system had lost electrical communication.
Then I shut the car off again, waited about 3 minutes, restarted it, and everything was back to normal with no warning lights at all.
I also spoke to another Mercedes workshop (not the one that replaced the brake switch and relays), and they told me that faults like this can be very difficult to trace, and that the only real way to find the exact cause would be to go through the wiring loom properly.
At this point, the only other suggestion I’ve been given is possibly the ABS pump / ABS module, but I honestly don’t know what to think anymore.
The fuses and connectors have already been checked, but nothing has been solved.
What I find really strange is this:
Every time the brake switch was replaced, the fault disappeared for several days
The same thing happened after the relays were replaced
Which makes it even more confusing.
If anyone has seen this before — maybe wiring, SAM, ground issue, ABS module, or something else — I’d really appreciate any advice.
Thanks in advance.
The issue.

 

Made an account to reply. It’s your illumination controller/fusebox. Mine did exactly the same stuff.

 

Thanks a lot.
Today I finally managed, using iCarSoft MB v4.0, to run a more complete diagnostic, both with autoscan and by individual modules.The report shown in the attached photos came up. I’d like to add that the issue that occurred today did not involve both the bulb warning light and the BAS/ESP light, but only the latter. Moreover, once it appeared, I was no longer able to activate the ESP using the button below the radio.Aside from this, the diagnostic also shows other fault codes (I don't remember what they are, I




can't find records of them of the previous diagnostic) about radio (but It works well) and air conditioning (but It works well too). I haven’t yet had the chance to run a diagnostic while both warning lights (bulb and BAS/ESP) are on, but this might already point to what you mentioned earlier (including the 255 bar reading, which fluctuates between that value and zero even when measured at a standstill), namely an issue with the yaw rate sensor N64 (which I believe may need to be replaced).I’m also considering cleaning the contacts in the fuse boxes in addition to replacing the sensor, but it’s possible that replacing the N64 alone will solve the problem.