HV DC/DC converter N83/1 HV voltage divider, reduction in resistance leads to BUCK mode fluctuations and ESP warning message
Topic number

LI42.45-P-079407

Version

2

Function group

42.45 - Electronic stability program (ESP)

Date

9/15/25

Validity

243 EQB

Reason for change

1). Standardization of the designation across similar LIs
2). Addition of the diagnosis procedure

Complaint
Instrument cluster warning lamp and/or warning message for brake system, EPB, ESP (yellow or red) and possibly 12
V battery (red)
Different combinations of the following DTCs present in the ESP: B23AA77, B23AB77, B23D177 and in part
(C100BE0, C100BE1, B23AA1B, B23D152)

Attachments
File

Description

DCDC KAMAYA Parkbremse Meldung KI DE.jpg

Warning message EPB, German

DCDC KAMAYA Parkbremse Warnmeldung rot englisch.png

Warning message EPB, English

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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
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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:
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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

Attachments
File
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Description
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EPB Aktuator Sicherungsring gebrochen.jpg

Actuator, retaining ring (possible malfunction)

DCDC 243 XENTRY BUCK mode Ausgangsschwankungen edited.mp4

BUCK mode fluctuations

DCDC Ausgangswert ok edited.mp4

BUCK mode ok

Disclaimer
NOTE: The information contained in this document is intended for use by trained, professional technicians with the
knowledge to properly and safely perform diagnosis and repairs on Mercedes-Benz vehicles, using Mercedes-Benz
approved tools and equipment. It informs service technicians about conditions that could occur in certain vehicles and
provides information that could assist in proper vehicle diagnosis, service, or repair. It does not indicate that a defect
is present in any vehicle referenced in this document nor does it imply warranty coverage. DO NOT assume that a
symptom or condition, or a described cause of a symptom or condition, affects any particular vehicle or groups of vehicles, or that a described repair applies to any particular vehicle or groups of vehicles. There can be multiple causes
resulting in the same or similar symptoms or conditions described in this document, and trained professional service
technicians must use their diagnostic skills to make evaluations on a case-by-case basis. The information contained
in this document does not guarantee warranty coverage nor does it extend the vehicle’s warranty in any way.

Symptoms
Chassis/suspension > Brake system > Parking brake > Indicator lamp > Parking brake > lit
Overall vehicle > Power supply > Battery/On-board electrical system > Battery/on-board electrical system display
message > Battery/Alternator - Serviced Required

Control unit/fault code
Control unit

Fault text

N30/4 - Electronic stability program (ESP®) (ESP177)

B23D152 - The brake calipers have a malfunction. The
component has not been put into operation.
B23AA1B - The left brake caliper has a malfunction. The
limit value for resistance has been exceeded.
C100BE1 - The electric parking brake has a malfunction.
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C100BE0 - The electric parking brake has a malfunction.
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B23D177 - The brake calipers have a malfunction. The
commanded position cannot be reached.
B23AB77 - The right brake caliper has a malfunction. The
commanded position cannot be reached.
B23AA77 - The left brake caliper has a malfunction. The
commanded position cannot be reached.

Operation numbers/damage codes
Op. no.

Operation text

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Time

Damage
code

H

54720

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Note

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