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Check engine light - looking for some thoughts. P0305 DTC code

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So, low milage car.  Took it out aprox 2 weeks ago, have not driven it in awhile and had low battery - dash flashed something like emergency start on start up.  Ran ok.  Started again 2 hr later after apt., weak start, no error message on start up.  Went for a spirited drive for about an hour to run up the battery.  2 min from home, goosed it a little to run it up one last time and I got the check engine light...  Back from the shop.  They tested the battery as ok under load but got a P0305 on cylinder 5.  swapped the plug and coil and so far after a 10 minute ride, no more code.  So, trying to understand this and im not a big engine guy-----


could the code be anyway related to the poor start up those last 2 times before the CEL?  Just keep running it and see if I get a repeat on the error code?  


Looking for some insight from others more experienced.  Shop says if I get the code again and its just a plug or coil, they recommend changing them all out - estimate 1400.00 - dearer price.  if its a code again on the same 5 cylinder could be bigger issue.


Last time new plugs and updated coils was 2016, 40k miles.  Now have 44k miles....    Thoughts please.  Tks much

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2 minutes ago, Loren said:

Could have been just a poor/dirty/loose connection by the coil pack.

I would not worry unless it comes back.

ok.  tks much.  No relation to the battery msg?

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I have said it before... all kinds of strange things happen now on cars with weak batteries.

The newer cars have a lot more electronics so I recommend that people replace a weak battery when it is 4-5 years old. Or, if it fails an (out of the car)  load test.


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When you say "swapped" coil/plug - do you mean for another position? If so, it will be interesting to see if the code follows it. Then you'll know.


How old is the gasoline in it? Even couple-month-old gas can be "flat". And cause misfires. Generally though, not at a single position (unless of course it was on the "edge").


I think there's consensus to change the plugs around 40k miles or 4 years, whichever comes first. It's my understanding the 4 years is motivated by trying to avoid damage to the aluminum head because the plug threads adhere themselves to the head threads.


If you're a DIY-er, changing the plugs is probably about a 6 of 10 difficulty. Don't need a lot of fancy tools. I've done mine. Your hands will be sore the next day. Two or three of the positions are especially onerous. Maybe a 2-4 hour job. I didn't even remove the mufflers. My car was up on QuickJacks. You'll save a bunch of that $1400. Especially if you already have the new style coils.


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thanks guys.  Yes, they took the 5 plug and moved the coil to another and the plug to a different cylinder.  4 and 6 maybe - don't have the paperwork here.  I just the other day watched a pca vid where the guy changed the plugs while changing out the exhaust.  looks much easier w/o that it the way.  id like to do it but ill need to find a lift.  ah, something to do....

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