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Discussion Starter · #1 ·
Our Elantra was "missing". The check engine light did not initially come one. It finally did, and it said P0301. I replaced the 1st ignition coil, and that seemed to have fixed. Recently, the same symptoms started again. The check engine briefly came on, but then went off. When it came on, I have having trouble accelerating up a hill. Should I replace ALL of the ignition coils?
 

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Do not blindly replace parts, this will only make your wallet lighter. If the light came on the code should be stored. You can have it read at any of the large auto supply houses.
If it is the same code it's time to look at spark plugs.

How many miles and have you replaced plugs/coils before on it?
 

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Our Elantra was "missing". The check engine light did not initially come one. It finally did, and it said P0301. I replaced the 1st ignition coil, and that seemed to have fixed. Recently, the same symptoms started again. The check engine briefly came on, but then went off. When it came on, I have having trouble accelerating up a hill. Should I replace ALL of the ignition coils?
Always troubleshoot before replacing parts. For example, before replacing coil one… swap coil one to another position with another coil. If the code moves to the new spot you know it is a coil problem. If it stays at coil one, look at a defective spark plug, fuel injector, fuel injection wiring or connector, coil wiring harness or connector, or bad compression on that cylinder. Good luck!
 

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Discussion Starter · #6 ·
How do I begin troubleshooting if the "check engine light" isn't on? It came on briefly the other day, but that was it. Someone mentioned that the codes are stored. I plugged up my OBD and it didn't find one. Would another OBD find it?
 

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How do I begin troubleshooting if the "check engine light" isn't on? It came on briefly the other day, but that was it. Someone mentioned that the codes are stored. I plugged up my OBD and it didn't find one. Would another OBD find it?
I would think all car makers have the option to read previous/pending fault codes as long as they have not been cleared, but maybe not.

If it is still running bad but no codes that does present a challenge. First do a visual inspection to make sur ethe coils and plugs look good and are seated correctly. If it is rough at idle you could unplug one coil at a time and see if it changes the way it runs. Beware if you unplug it while the car is running you could get shocked and it does sting a bit.
 

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I had the same problem in my 2018 Elantra GT with GDI...Turned out to be 2 bad injectors...This happened after I used some stuff I bought at the Dollar Tree to increase mileage....Even injector cleaner wouldn't fix it...Very interesting this GDI...
 
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