Coolant Intrusion in Mercedes EQ High-Voltage Battery Systems: Causes, Diagnostic Indicators, and the Risk of Unnecessary Battery Replacement

Samoilov Alexey

Citation: Samoilov Alexey, "Coolant Intrusion in Mercedes EQ High-Voltage Battery Systems: Causes, Diagnostic Indicators, and the Risk of Unnecessary Battery Replacement", Universal Library of Engineering Technology, Volume 03, Issue 02.

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

The rapid expansion of the global electric vehicle market, which surpassed 17 million units sold in 2024 according to the International Energy Agency, has made the reliable diagnosis of high-voltage battery faults a critical competency for automotive dealerships worldwide. In Mercedes EQ vehicles, coolant intrusion into the battery enclosure represents a frequently underdiagnosed failure mode that shares its primary symptom with genuine cell-level degradation: a drop in isolation resistance triggering Battery Management System fault codes. The present study examines the technical causes of coolant ingress in EQ platform battery systems (EQA, EQB, EQC, EQS, and derivatives), characterizes the diagnostic indicators that distinguish this event from primary battery failure, and evaluates the downstream risk of unnecessary high-voltage battery replacement. Through systematic review of manufacturer recall documentation, technical service bulletins, peer-reviewed literature on battery thermal management and fault diagnosis, and documented dealer case studies, this paper shows that coolant intrusion can depress isolation resistance to levels that trigger emergency shutdowns without causing irreversible cell damage. A structured six-step diagnostic protocol and a replacement decision matrix are proposed to guide technicians. The findings are of direct relevance to Mercedes-Benz authorized dealers, independent EV specialists, and automotive service engineers seeking cost-effective, evidence-based diagnostic workflows.


Keywords: Coolant Intrusion, High-Voltage Battery, Mercedes EQ, Battery Management System, Isolation Resistance, EV Diagnostics, Thermal Management, Dealership Service, Fault Code, Battery Replacement Risk.

Download doi https://doi.org/10.70315/uloap.ulete.2026.0302016