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Mercedes W205 C300de (2019) – Hybrid System Malfunction, Inverter Fault P0A7800, No S
Hello, I am looking for expert diagnostic assistance with a Mercedes hybrid system fault.
Vehicle: Mercedes-Benz C300de (EQ Power)
Model: W205
Model year: 2019
VIN: WDD2050131R544076
The vehicle repeatedly displays the following warnings:
• Hybrid system malfunction
• Coolant too hot – stop vehicle
• Without starting engine again, consult workshop
The car frequently fails to start. When it does start, the ICE and hybrid drivetrain behave abnormally, and the system quickly returns to fault/limp mode.
Fault codes (Xentry / Autel):
• P0A5FFA – Electric machine A, phase U current too high
• P0A62FA – Electric machine A, phase V current too high
• P0A65FA – Electric machine A, phase W current too high
• P060AFB – Control unit monitoring function malfunction
These DTCs indicate a likely power electronics / inverter-related fault, possibly caused by:
• Internal inverter failure
• Short circuit or insulation breakdown in the high-voltage (orange) wiring loom between inverter and electric motor
• Coolant ingress into the inverter or malfunction of the inverter cooling circuit, leading to overcurrent protection
I have attached photos of the fault messages, diagnostic readouts, wiring diagrams, inverter location, and HV wiring loom (part numbers A2055406521 / A2135455400) for reference.
Before replacing the inverter, I would like confirmation whether this issue is commonly caused by HV cable insulation damage, connector corrosion, coolant intrusion, or other known weak points on W205 C300de models.
If you have hands-on experience with similar cases or can advise on the correct diagnostic procedure (insulation resistance tests, phase resistance values, HV safety checks), I would greatly appreciate your guidance.
I am happy to continue via WhatsApp and I am willing to pay for professional diagnostic support.
Thank you for your time. This could be the cable causing this whole issue? Its is located under the car and connects to the inverter. These are the faults that come up as well when i start the car and everything comes on at once, after about 30sec to 1 minute of idle.
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