I have an '03 MCS with the typical trifecta lights. I have replaced the ABS sensors. There are three strange things about this case. The problem is intermittent, happening about 25 percent of the time. Second, I can get the trifecta to occur about 80 percent of the time by turning the headlights on quickly. Lastly, every once in awhile, the ABS pump or something causes the pedal to feel like it is engaging, with the accompanying shudder. I have searched, but I have not seen this one. Thanks for any help.

 

Check your battery voltage: key off, key on, engine idling and headlights off, engine idling headlights on. Weird electrical issues are typically caused by a failing alternator or battery. There is a instrument cluster test that tells you the voltage, or you can use a multimeter, or most auto parts stores will test your battery and alternator for free. I recommend the last because you may have good voltage but poor quality voltage (high ripple) caused by a bad alternator.

 

I've been chasing a TRIFECTA issue for several months now and am still stumped.

Your issue brings up an interesting question.

can the ABS trifecta be triggered by the leveling system for the headlights?

The reason I ask is this. Over the past several months I've replaced my drivers side control arm, drive shaft, bearings, tie rods etc. When replacing the control arm I notice the mount for the headlight leveling was bent badly, it was in such a position that it cut through the CV boot and ruined the axle.
I replace the axle, straightened the mount for the leveling sensor and reinstalled.

I replaced the ABS sensors at all four wheels, everything checks out. but still have the "three lights from hell". could the Leveling sensor have anything to do with this problem?

if yours in coming and going when the lights are on, it makes me wonder

 

Leveling sensor has nothing to do with DSC, it just tells the headlights when to move.
The headlight leveling isn't causing anything, but the headlights and all other lights getting turned on could cause the system voltage to drop low enough that the DSC goes into failsafe mode, I think this happens around 11.5 Volts.
If the battery and alternator are ok, have a shop or someone with a good code reader download the faults from the DSC module. Too many possible causes in the DSC to just guess and replace things like speed sensors.

 

racingbmwm3

thanks, it was just a crazy thought.

there seems to be several approaches to this, didn't know if this might be one

 

I've got a Trifecta that only kicked in when driving 125+ kph with my 16" wheels, of 130+ kph with my 17" wheels. Weird huh?

 

very. stock suspension? if aftermarket, alignment outside factory specs (toe) could cause DSC to freak out.

 

Stock suspension. Doesn't seem to have an alignment issue.

 

only other guess would be extremely dirty wheel speed sensors?

 

Yeah, I figure it's the actual sensor myself. I'm new to the car, so I'll have to squat down and take a look at everything when it's waxing time. (if it would just stay nice here on a weekend!)