Quote:
Originally Posted by 986 Boxster
Yes you're right, you don't get a code for a coil being bad, but you do get a code for a miss fire, and 99% of the time it's a bad plug or a bad coil. So it's very simple to figure out if you have a bad coil or a bad plug. Let's say you get a code for cylinder #4 for example, all you have to do is change a coil from a different cylinder to #4 and you will know if you have a bad coil or a bad plug. If the code comes back to cylinder #4 you know you have a bad plug, but if the code comes back to the cylinder that you changed the coil to, you know it's a bad coil  |
All true if you have a bad plug or bad coil.
You could also have a coil wiring issue on cylinder #4
You could also have a fuel injector issue or injector wiring issue on cylinder #4
Or valve train issues on cylinder #4 ect.ect.ect.
And get the same #4 cylinder misfire code.
My point to the OP was there is no CEL or OBDII codes that tell you a coil is faulty.
Misfire codes are triggered for many reasons depending on frequency and severity of the misfire.
The reason for the misfire as you pointed out has to be determined by diagnostics.