usually it comes on if ur battery charge is getting low. I had a problem with my abs light flickering while i'd drive, and my problem turned out to be a faulty OVP. So you might want to look into both of these items.

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My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems