Mercedes W221 S400 no start

Repair Help Mercedes-Benz
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1

Hi

My Mercedes W221 S400 Hybrid has decided not to start. There has been an intermittent problem for a long time where the car sometimes needed two to three attempts to start but now it’s permanent. I have read the Youcanic articles and have a feeling it could be the Power Electronics Module but still not sure. The hybrid battery charge is 54% and the voltage is even over all cells.

There are the following fault codes that I didn’t notice before:

Engine ECU: No codes.

DC/DC converter: U010000; Communication with the ECU has a malfunction.

BMS: C11000; Communication with control unit Electric machine A has a malfunction.

Power Electronics Module: P0A1E00; Component N129/1 (Power Electronics Control Unit) has a malfunction.

There are also the following codes that were present when the car still started:

BMS: 0A7F00; Age limit of the high voltage batteri module is reached.

BMS: 0A8000; Component A100g1 (High voltage battery) is defect.

Hoping that you can give me a better idea of what could be wrong.

2

Based on the fault codes that you have posted, you have both a faulty power electronic module and also a faulty hybrid battery.

3

Hi
Check the wires and conectors for corosion or water demaged.

4

Thanks for the input guys, I will definitely check wires and connectors. Any known spots to check first? If it comes to replacing parts, can I start by replacing the Power Electronics Module and see if that solves the problem or do I have to replace the BMS at the same time to not damage the new PEM?

6

Hi sir, It sounds like your W221 S400 Hybrid has an issue with the Power Electronics
Module (PEM) or related communication systems. The P0A1E00, U010000, and C11000
fault codes point to a malfunction in the PEM or DC/DC converter. The BMS codes
suggest aging in the high-voltage battery, but since the charge is stable, it’s
likely not the immediate issue.

I recommend focusing on the PEM and inspecting wiring and connections for damage
or corrosion. To pinpoint the issue, use a YOUCANIC Scanner for detailed live
data and accurate diagnostics. It’s a great tool for hybrid systems and can help
confirm if the PEM needs replacement or if another component is at fault.