2004 coupe, 30k miles ...runs perfect.......drove 50 miles to friend.....no issues whatsoever......On my way back home , the esp/bas light came on. ....after a few miles, I pulled over and did the steering lock to lock drill,
Shut it off, restarted and headed out again......with in 1/ 2 mile, light came back on again. When I got back home , I did the steering deal again.....light went out....pulled into the garage and let it idle.....within a minute , light came back on. Shut in down and plugged in my NEXPEAK NX501 reader.....no active or stored codes........The brake light switch and the "yaw" sensor have been mentioned a possible causes.
Where do you start ? what has been the most common culprit ? p/n's..? source ? When I bought the car from original owner at 24k miles, I did a complete brake upgrade with new cross drilled /slotted rotors, pads, and wear sensors. All new Continental Extreme tires. Car is perfect, garaged all winter . It's a great car.......very uncommon in my area. I don't mind replacing parts if needed......but not on a trial and error process. Any help appreciated.

 

SRT? If not, does the wing stay in the UP position when you get the fault?
If yes then it could be the traction control relay in the RCM.

 

The most common culprit is the brake light switch and it's best to get a genuine Mercedes (0015456409 for the automatic transmission). You might want to try another code reader to see what the exact code stored is. My MB II code reader couldn't read the BAS/ESP modules when there was a code but zero problem with no codes stored. The Autel MD802 was able to read the code as a Mercedes SLK320. The brake light switch code can be stored in the BAS/ESP modules and one time it was stored in the transmission module.

When the light is on, if your brake lights do not light up when depressing the brake pedal or the cruise control does not work then for sure it is the brake light switch. Otherwise it is best to see what the code is first.

 

~ How soon after your brake upgrade did the problem first occur?
~ The brake light switch is around 20 bucks. I got mine from either Rockauto or FCPEuro, or WorldPak at Advance Discount Auto.
~ There is a sensor wire that needs to treated gingerly (what's that mean?) when doing brakes as I recall. Be careful with positioning it into its slot.

 

When my light was on, the cruise would not work. The brake pedal switch did the trick for the repair.

 

When I went to bleed my brakes after installing a new ABS module my BAS/ESP lights came on to as a direct result of me bleeding the brakes, I had to use my iCARSOFT i980 to clear the codes from the brake assist module and only then did the light turn off.

The CAB connector (47 pin connector) bridges together the BAS module and ABS module and that connector alone is a Huge disturber hub for a lot of other connections in the car and in my case was the root to all of my issues. I had no speedometer or speed functions, and the ABS, BAS/ESP, CEL, Brake wear indicator light, and hand Brake light were all on.