The electrohydraulic brake system of the early W211 E-Class (and the related C219 CLS), the SBC, can switch into hydraulic backup mode because of software and hardware faults, with a longer pedal travel and more effort needed. The maker started several recalls (NHTSA 05V133 and its predecessors); the 2006 W211 facelift already got conventional hydraulic brakes, and the SBC was dropped because of complaints.
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After the recall is closed, the SBC pump unit still has a service life counter, the replacement is expensive, and the backup mode is noticeable on a test drive. On the post 2006 facelift W211 this system is gone.
What to check
- Only the pre 2006 W211 and early CLS C219 are the subject: the facelift got conventional brakes
- Try the brakes cold and after several hard stops: a suddenly "long" pedal or more effort suggests backup mode
- Watch the dash: an SBC warning message calls for immediate expert inspection