A battery may have a single cell breakdown, resulting in a charging voltage that is accurately measured while the engine is running but drops below the "Fully Charged" threshold level when the engine is turned off. The ECO-drive will only function if the "Fully Charged" status flag is set. However, it is worth noting that this specific kind of cellular malfunction might still allow the vehicle to start smoothly and there will be no indications of alternator issues on the dashboard or any Diagnostic Trouble Codes (DTCs) being triggered.
An exhaustive diagnostic examination should include a load test, which involves subjecting the system to a brief period of intense strain, imitating the stress experienced during engine cranking. Additionally, it is crucial to measure the battery voltage when the engine is running and all electrical consumers, such as the infotainment system, heated seats, headlights, and air conditioning/fan, are activated at a certain engine RPM. This is done to eliminate any potential issues with the alternator.