Hi, any insight into the issues with my vehicle would be much appreciated I have a 2021 Land Rover Discovery 5 R-Dynamic S P360 that is experiencing Voltage Drop-

Looking for help narrowing down root cause between alternator and DC-DC converter.

Symptoms & scan data:

12V battery voltage drops immediately after startup

• Alternator output: ~1.2V, 0A field current
• DC-DC converter output: 10.5V–11.1V, 0A current
• ICON scanner shows:
  • BECM fault code
  • Gateway Module A – “voltage below threshold”
  • Quiescent Relay Box Relay 1 shows 135 open events
    Battery sensor appears to be reading correctly — state of charge is fine, and quiescent current is ~100μA.

Trying to determine:

• Best way to test DC-DC converter vs alternator in isolation

Any insight appreciated before throwing parts at it.