My fried told me that my 4th gear in my ford explorer is going bad, he put a plug in to test things?

My fried told me that my 4th gear in my ford explorer is going bad, he put a plug in to test things?

He' is correct

Your "FRIED" told you this? No, Skippy… You're NOT going to diagnose a transmission problem from reading the codes from the ECU.

Ford Explorer, yes the transmission is going bad. Don't need some fancy electronic magic to know that.