I was driving my s5 and the tach went out, then the check engine light came on. I pulled a code 1 wich is a trailing coil. I disconnected it and cleaned all the grounds and the checked all the wires. When i put it back together it was working for the first 15 min of driving then went out again. Do you think the trailing coils went out?

 

Yes.
"-ted"

 

I was just puzzled because it was working once i hooked it all back up, then it stopped agian.

 

you check the ground underneath the coil? Check Aaron Cake's grounding tutorial