If Minato was a chakra sensor

[LUMOS ULTIMATUM]

Why did he not recognise tobi's chakra as obito during the nine tails attack?

 

[Unorthodox]

because he isnt

 

[Touken]

He had Senju DNA covering up the right half of his body, and I'm pretty sure your chakra signature changes when you become more malicious.

 

[Dribbles]

He had Senju DNA covering up the right half of his body, and I'm pretty sure your chakra signature changes when you become more malicious.

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[Avinash012]

More darkness = more changes in chakra of Uchiha's as noted by Karin in case of Naruto on top of that Obito has Senju DNA.

 

[juankimari]

Why did he not recognise tobi's chakra as obito during the nine tails attack?

Basically the same thing that happened with Kabuto in the latest chapter.Obito had zetsu literally infused to half his body.

 

[Champ]

He has to focus and turn on his sensing ability.

 

[EKSITE]

Well Obito did have have Hashirama cells covered around his body & you got to remember acouple of chapter ago minato didn't have his chakra sensing ability on he probably doesn't fight with it on.