ok so ive been havin this prob with my car for awhile now,
the car runs great drives great but once in awhile the tach shuts off and the check engine light turns on , car still runs and drives just no tach.
any ideas?
trailing coil?

 

check for spark on the Coils, I think the tac is linked to the leading. But im not for sure. ill have to look in a sec, a coil pack could have went dead? or came loose. how does it run?

 

no noticable difference

 

o its an s5

 

Its an intermittent problem? does it happen on hard corners? possibly loose wire or maybe a Bad Fuse? check the sources, Fuse then coils check connections between all of it, It throws a check engine light? try to figure out what code its throwing

 

ya its intermitent, mostly in corners, what fuse? they are all good. if i turn it off and back on the check engine light does not come back on so i couldnt check the code

 

You said it quit working.. but Now you say its intermitent.. Glad noxi was around to spill the beans.

 

intermitent/ works for a little bit then turns off, if i turn the car off then back on sometimes it comes back on somtimes it doesnt, only if i turn the car off i havent seen it turn itself back on
sorry i didnt make that clear

 

im gonna try checking the coils tmw when running/with the tach not working and go from there

 

Cars some time do now like to "play right" when your doing your testing, as soon as you get the problem Test it asap if you can, if the coils fire then move on to the next problem like the connection from the Tach to the coils, I honestly dont know what fuse but you said it happens in corners, which makes me assume its a loose wire dangling about or grounding out I hope you figure out your problem, If you cant find the issue post in the actual 2nd gen section alot of people will help you try to determine what the problem is

 

i will thanks

 

first start by checking codes, preferably when the issue is present.

next try swapping the TRAILING coil with a known good one, as that is where your tach signal comes from, not the leading.

if all else fails to point you in the right direction, pull the cluster out and inspect the wiring, i have seen some cars with corrosion on the pins to the printed board for the cluster, unplug it and plug it numerous times. if that still doesn't work then the studded connections for the tach may be corroded to the point of a bad connection, you can clean them or simply replace the instrument cluster.

 

thanks ill try that

 

Clean all the connections on the trailing coil.

 

found the problem, the leading coil went bad
thanks for the help

 

I went to look.. the leading Coil pack is Nearest to the BAT.. so yea the Tac is Hooked to the Coil nearest the battery

 

not really, unless it has an aftermarket tach hooked to the RPM signal port on the leading coil.

the stock tachometer is wired directly to the trailing coil nearest the firewall.

i could envision if the whole ignition system was cutting out the tach would be failing but the car would not be drivable.

 

i dunno.. Mine is stock.. and the tac is hooked to the coil that is nearest the bat.. Edit. Your Right there is an after market hookup to the leading coil back, I just remember one time not to long ago Turning of the leading coil pack to test somthing and noticing my tac not working.. but i could be wrong

 

Yes. You were Right..I found my Stock tac hookup. it is infact on the trailing coil nearest the firewall. My eyes buggin

 

i thought a coil pack went bad, turns out the round plug on the back of the instrument cluster was loose / not making contact. i used a small flat head screwdriver and pinched them closed and it works alot better now.
thanks to all that responded.