Mercedes GLA Diesel Electrical Fault Diagnosis

An intermittent Terminal 30 fault on a 2014 GLA diesel is vexing. Have you performed a parasitic draw test to ascertain the magnitude of the current drain when the vehicle is at rest? What is the battery voltage immediately after shutdown, and again after sitting overnight? This data will aid in discerning whether a component is failing to power down correctly, or if the battery itself is compromised. Please provide more details for a thorough diagnostic assessment.

I did perform a parasitic draw test and saw a significant voltage drop after about 30 minutes. Voltage after shutdown is around 12.6V, but it dips to 11.8V overnight. Do you think this definitively points to a short circuit somewhere, or could it still be a faulty circuit breaker causing the issue?

Given the voltage drop overnight, a parasitic drain exceeding acceptable limits is probable. While a faulty circuit breaker may contribute, the magnitude of the drop suggests a more substantial current leak. To avoid further complications, it is recommended that you consult a qualified technician to use specialized diagnostic equipment to isolate the failing circuit. This will prevent further damage to vehicle systems. Proceed with caution!

I appreciate the detailed advice. I took it to a trusted workshop. They confirmed a faulty auxiliary battery was causing the parasitic draw. The repair cost was 290€. Thanks again for pointing me in the right direction!