The ESP lamp went off in my mother's E430.

I checked her owner's manual, and it said that is voltage goes below a certain level, the lamp will be illuminated.

The fix was to turn the steering wheel from left to right so that the system could "relearn", or something to that effect.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".