P0301 code
 

My HHR check engine light popped on yesterday in my '06 HHR (112,000 miles). Code P0301 (random misfire cylinder 1) read at Advance Auto. No driving issues when on, no driving issues prior. I was getting 30mpg + driving on the interstate, I had the code cleared and it didn't come back.

Of course I'm 600 miles from home and have another 600 miles to go, before returning.

Any ideas if this was just a random hiccup or something to be concerned about? This was the first check engine light I've had with the HHR. Plugs (AC Delco) were replaced at 60K miles.

You may have a failing ICM (Ignition Control Module), 2006's are unique in certain key areas....one of which is the ICM. Keep an eye on it, if the CEL comes back, I'd get to a dealer for a diagnostic check.

I drove another 700 miles and no more SES light and getting 30+ mpg.

Sounds like a spurious CEL, keep a eye on it and have safe travels.

843de made some good points. It could have been a bit of moisture in the gas - or just that spurious CEL as he said.

It may be time to think about changing the plugs again, as they have 52,000 miles on them, but they should last a little longer than that.

If it does pop up again, I'd swap plugs and also swap the coil to a different cylinder yet, and see if the problem moves. ie: swap plugs between cyls 1&2, and swap coils between 1&3 to help pinpoint the problem.

Still no re occurance of the error code. Of the last four fill up, my mpg has been some of the best I've had in recent years. 35-38 mpg. But mostly highway @ 55-65 mph.

I ended up changing the plugs (116,000 miles) even though the error code never came back. I did have about 59,000 miles on those plugs. I don't believe the 100,000 spark plug life, but the plugs coming out still looked good. A busy driving month about 4000 miles.