Check Engine Light is On

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Old 04-20-20, 04:45 PM
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Check Engine Light is On

The other day, I noticed the check engine light on for our 2013 Sonata.

I borrowed my neighbors ODB2 Scanner and checked it.

The codes are p303 (cylinder 3 misfire) and p304 (cylinder 4 misfire)

My neighbor said if the car has been sitting, and it has been due to COVID-19 stay at home orders, it may be moisture in the tank (tank is filled). He said to fill it up and run it on a few trips. It may reset the codes after 3-5 starts and taking it on 8 10 mile trips.

Any ideas on if I need to get this to a shop soon ?
 
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Old 04-20-20, 07:38 PM
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miles? these newer systems make it almost impossible to get water in the tank. and any slight amount that does is absorbed by the e-10/15 gas. I wouldn't stress about unless you see the light flashing or physically feel it miss/shutter. clear it with the scanner
 
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Old 04-20-20, 08:06 PM
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I agree. Reset the codes and run it.
 
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Old 04-21-20, 12:18 AM
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You need to understand that a code set does not always indicate a problem, it can just be a detection of a reading that is momentarily out of spec.

Take it into the dealer and your getting a nice bill, clear the code and run the car and see if it returns, 90% of the time they go away, if it's a real problem the code will come back!
 
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Old 04-21-20, 11:02 AM
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Just drive the car for a few days and see what happens, looking at a spark plug isnt going to tell you much about the internal engine controls!
 
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Old 04-21-20, 01:20 PM
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the OBD2 system has continuous misfire monitoring. The only thing with the engine controls that will cause a misfire is the crank sensor (on most cars) since its output is used to determine crankshaft rotation. If there were a problem with it, it would probably be throwing a P0300 multiple cylinder miisfire DTC. There will be a retained code for misfire the first time crankshaft rotational velocity varies by 2% or more but the CEL won't light up. It only lights up after a missfire is detected on 2 consecutive drive cycles.

Most of the time (from my experience) its the spark plugs, or the ignition coils.
You can tell all kinds of things by looking at the spark plugs. look up "reading spark plugs"

If the spark plugs look good, swap the coils on cylinders 1 & 2 wth the coils on 3 & 4. Clear the codes and drive it until the CEL lights back up. Scan it for codes, if the misfire is now on 1 & 2 (P0301, P0302), you will know those ignition coils are bad.
 

Last edited by user12386595; 04-21-20 at 01:51 PM.
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Old 04-21-20, 11:45 PM
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Light came on with my car at about 105,000 miles. I had meant to change the spark plugs at 100,000 but it was cold outside then. I replaced the air filter at the same time and the light went off about a week later.

I would start by comparing the owner's manual and maintenance checklist for the mileage you have on it.
 
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Old 04-23-20, 11:59 AM
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car has 114k.

We have ran it about 4 times since filling it with gas then today, my wife took it out and said the CEL light was not on.

I went out and started it and then tuned it off.

As the engine stopped and right after it stop i hear a noise up it the engine,,,video below...not sure if it is related as my wife never noticed it and i don't drive her car

https://www.youtube.com/watch?v=osAAh97HWzY
 
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Old 05-07-20, 07:59 AM
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after running the car for a few days, the codes cleared,,,,

I did notice this noise after the engine is turned off...may have been there all the time,.

Someone said,,
Sounds like drive by wire throttle body sweeping after engine shut off. Other cars do it and it is normal.

Just want to be sure....


https://youtu.be/J_iWzF0byfI
 
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