battery voltage problem

[alperx]

when the engine is not running : it shows 12v

when the engine is running : drops to 4v.

what can it be ?
thanks

4v.jpg (249.8 KiB) Viewed 664 times

[alperx]

note : all the voltages measured while the engine is running, they are between 13.5-14.0v , including the 3 battery cables going into the tcu.

[Jar]

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