Vehicle sporadically fails to start or can no longer be started
Topic number

LI54.10-P-054690

Version

3

Design group

54.10 Battery, voltage supply, voltage converter

Date

05-13-2014

Validity

Models 221.095 and 221.195 (Hybrid)

Reason for change

Capacitance limit increased from 800 µF to 950 µF

Reason for block

Complaint:
•
•
•
•
•

Combustion engine sporadically fails to start.
Combustion engine can only be restarted after a waiting period of approx. one hour.
Combustion engine can no longer be started.
Start/stop function is sporadically unavailable (READY displayed in yellow in instrument cluster).
Fault code "current and stored" in electric motor control unit (SG-EM) (see control unit fault code).

Cause:

Due to reduced capacitance of the high-voltage intermediate circuit capacitor in the power electronics (N129/1), the
hybrid functions (e.g. start/stop, boost, regenerative braking) may be deactivated. If the capacitance of the high-voltage intermediate circuit capacitor is severely reduced (less than 950 µF), engine start can be suppressed either occasionally/sporadically or permanently. Because of this, the 30A fuse of the HV battery (output to DC/DC converter) may
also have blown.

Remedy:

Requirement:
- Use a battery charger to ensure that the voltage supply of the vehicle's on-board electrical system battery is sufficient (greater than 12.5V)..
Work instructions:
1 Check fault memory in electric motor control unit (SG-EM) for phase errors.
If at least one of the following fault codes (FC) is present in the SG-EM control unit with status "stored" and/or "current
and stored", the SG-EM control unit must be replaced and the test terminated (steps 2 to 5 should not now be performed):
- P0A5D00 The connection 'Phase U' of electrical machine A has a malfunction.
- P0A6000 The connection 'Phase V' of electrical machine A has a malfunction.
- P0A6300 The connection 'Phase W' of electrical machine A has a malfunction.
2 Check software (SW) in SG-EM control unit and update if necessary (ring flash: SG-BMS, SG-DDW and SG-EM).
If SW version 12.04.00 is present in the SG-EM control unit, continue with step 4. If older software is present, install
the latest software.
To do this, select menu item “Control units – Drive – SG-EM electric motor control unit – Control unit adaptations –
Control unit programming”. After the software update, return to the control unit groups menu item.
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3 Determine total capacitance in electric motor control unit SG-EM.
3.1 Create SG-EM control unit log. To do this, select menu item “Control units – Drive – SG-EM electric motor control
unit – Control unit log” and create the control unit log. Then read off the value “Average value of total capacitance” in
the SG-EM control unit log. If a value of 0 µF is shown, continue with step 3.2. If a value greater than 1µF is shown,
continue with step 4.
3.2 Start combustion engine and switch off again (or circuit 15). Remove ignition key and leave removed for at least 2
minutes. During this period, do not operate any electrical consumers and leave all doors/flaps closed (wait for bus idle). DAS/XENTRY and battery charger remain connected. This procedure must be repeated six times! Then perform
a "control unit reset" (to be found under "Actuations"). Afterwards create another SG-EM control unit log and read off
the value “Average value of total capacitance” in the SG-EM control unit log.
4 Evaluate total capacitance (value “Average value of total capacitance”) from SG-EM control unit log.
If the average value is less than 950 µF, the power electronics must be replaced.
5 Check 30A fuse of HV battery for proper operation (continuity test).
The test can be found in DAS/Xentry in the battery management system control unit (SG-BMS) at the following path:
“Troubleshooting via complaints and symptoms” => “Initial startup of high-voltage on-board electrical system not
possible. Voltage of high-voltage on-board electrical system at component N83/1 (DC/DC converter control unit) = 0
V.”
If the 30A fuse is defective, the HV battery must be replaced.

Symptoms
Overall vehicle / Power supply / Battery/On-board electrical system / Battery function / Battery discharges
Power generation / Engine management / Engine start/stop / Does not start
Power generation / Engine management / Engine management indicator lamp / READY indicator / Does not illuminate

Control unit/fault code
Control unit

Fault code

Fault text

SG-EM-Electric motor control
unit (SGEM)

P0A1E00

Component N129/1 (Power electronics control unit) has a malfunction.

SG-EM-Electric motor control
unit (SGEM)

P0A5D00

Connection 'Phase U' of electric machine A has a malfunction.

SG-EM-Electric motor control
unit (SGEM)

P0A6000

Connection 'Phase V' of electric machine A has a malfunction.

SG-EM-Electric motor control
unit (SGEM)

P0A6300

Connection 'Phase W' of electric machine A has a malfunction.

SG-EM-Electric motor control
unit (SGEM)

P0C0C00

The power supply of the high-voltage on-board electrical system
for inverter 'Electric machine A' has a short circuit to ground.

SG-EM-Electric motor control
unit (SGEM)

P160A00

The capacitor of the power inverter has a malfunction.

SG-EM-Electric motor control
unit (SGEM)

P160B00

There is a warning about the capacitor of the power inverter.

Parts
Part number

ES1 ES2 Designation

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Quantity Note

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EPC Other
ma-

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ke
part
A 000 906 47 03

Rectifier

1

Electric motor control unit (SGEM)

X

A 221 343 11 00

LI-ION BATTERY

1

HV battery (SG-BMS)

X

Work units
Op. no.

Operation text

Time

54-1011

PERFORM DAS QUICK TEST AND
ERASE FAULT CODE

08-1200

REMOVE/INSTALL POWER ELECTRONICS WITH POWER DISTRIBUTOR, REPLACE IF NECESSARY

54-1014

PERFORM POWER DISCONNECT/INITIAL STARTUP OF HIGH-VOLTAGE
ON-BOARD ELECTRICAL SYSTEM

83-1762

EXTRACT REFRIGERANT, CHECK
FOR LEAKS, REFILL

54-1153

REPLACE HIGH-VOLTAGE BATTERY

Damage
code

Note

5441B 73

Damage code: 5441B (high-voltage
intermediate circuit capacitor)

It is not necessary to replace the
fluid reservoir for this repair.
5441B 73

Damage code: 5441B (high-voltage
intermediate circuit capacitor) to be
used, as consequential faults arise
from a defective "high-voltage intermediate circuit capacitor".

WIS-References
Document number

Title

Note

Allocation

AR08.10-P-0011SXH

Remove/install power electronics with power distributor

Remedy

AR54.10-P-1140SXH

Remove/install high-voltage
battery

Remedy

Validity
Vehicle

Engine

Transmission

221.095

*

*

221.195

*

*

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