Diagnosing High-Voltage Faults: From the DTC to the Engineering Cause of Failure

Citation: Samoilov Alexey, "Diagnosing High-Voltage Faults: From the DTC to the Engineering Cause of Failure", Universal Library of Engineering Technology, Volume 03, Issue 01.

Copyright: This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

High-voltage electric vehicles now form a routine part of dealership service work, and a stored diagnostic trouble code is often treated as the answer rather than as a starting symptom. This manual sets out a practice-oriented method for moving from a recorded code to a proven engineering cause of failure across the high-voltage architecture of compact premium battery electric vehicles, including Mercedes EQ, BMW i and i3, MINI Cooper SE, and Smart EQ. The introduction frames the problem against current market data, where electric car sales reached about 20 million units in 2025 and roughly one in four new cars sold was electric. The method combines four steps: reading the high-voltage architecture and wake-up logic, classifying intermittent shutdown by operating phase, locating isolation faults through safe circuit separation, and verifying the cause with measurements, logs, and thermal data before any part is replaced. Results are presented as an authored confidence ladder that gates high-voltage component replacement behind convergent evidence. The conclusion confirms each aim and offers a reporting format for service, warranty, and the customer. The material will interest dealership diagnostic technicians, warranty engineers, and service managers.

Keywords: High-Voltage Diagnostics, Diagnostic Trouble Code, Isolation Resistance, Intermittent Shutdown, Pre-Charge and Contactors, HVIL, Freeze-Frame Analysis, Fault Timeline, Engineering Root Cause, Battery Electric Vehicle.

https://doi.org/10.70315/uloap.ulete.2026.0301022