Mercedes-Benz bulletin LI42.45-P-079407

Complaint Instrument cluster warning lamp and/or warning message for brake system, EPB, ESP (yellow or red) and possibly 12V battery (red) Different combinations of the following DTCs present in the ESP: B23AA77, B23AB77, B23D177 and in part (C100BE0, C100BE1, B23AA1B, B23D152) Cause Due to a reduction in resistance at the HV voltage divider, the DC/DC converter measures an incorrect HV voltage. Regulation of the 12 V output voltage therefore becomes unstable. I.e. the output voltage starts to fluctuate and the output current starts to jump instead of slowly regulating to the currently requested value. The EPB position is calculated by the voltage and the current. Since these fluctuate, the ESP control unit loses its position and sets the DTCs. Remedy Check of the DC/DC converter via XENTRY Diagnosis • Actuate BUCK mode for approx. 40 s • The output current normally jumps to a high value (e.g. 100 A) and then falls slowly to the current specified value e.g. 50 A and then only changes slowly and in small increments. • In the event of this fault cause, the output current is subject to strong fluctuations/jumps (multiple 1-10 A) (see videos in attachment) • Perform in XENTRY -> DC/DC converter N83/1 -> Special procedures -> "Evaluation of the HV resistance reduction of the DC/DC converter control unit". The special procedure compares the serial number of the installed DC/DC converter with the list of potentially affected parts. • Depending on the result: • If the serial number can be found in the list of potentially affected component parts, then replace the DC/DC converter. • If the serial number cannot be found in the list of potentially affected parts, XENTRY reports that the part is not malfunction. If the problem from this LI applies, please open a TIPS case and forward to HQ. Subsequent complaint, malfunction on the EPB: • Check of the actuators and brake caliper piston • Manually extend and retract the piston on the brake caliper completely using the suitable socket • If the piston sticks at a certain point, the rotation force increases significantly • If the brake caliper piston sticks, the brake caliper has to be replaced • If the retaining ring of the actuator is broken, the actuator has to be replaced • In XENTRY, edit the stored test instructions of the remaining DTCs

Owners of the 4 model years this bulletin names have filed 134 complaints with NHTSA since 2015. 104 of them name Electrical System — the same broad component group this bulletin is filed under. NHTSA groups complaints coarsely, so that means the same area of the vehicle, not necessarily the same fault.