Why is my check engine light coming on after highway driving?

Question

My pontiac g5 is getting this p0300 code only after driving on the highway (which is most of my driving). When I am off the highway for 10 miles or so it turns off. I have no other symptoms than the check engine light. I have ran seafoam and lucas injector cleaner through the fuel system, but do not want to start changing all sorts of parts without knowing what is causing the issue.

Answer 1

Hi there

It sounds like you may have a bad ignition coil. The computer is seeing a misfire, but can't determine which cylinder has a problem. Sometimes the coils will only misfire under the right circumstances, seems the higher engine rpms and higher speed could be the time the coil misses. You might not feel the issue at a higher engine speed and may have to wait until the coil gets a little bit worse before you can determine which cylinder is the problem.