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Unread 01-21-2014, 01:21 PM   #1
jhc09
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2009 JK Wrangler 
 
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Got a P0 300

Started up my 2009 JK yesterday and noticed some rough idling, then the engine light came on. I just hit 25,000 miles. I went out at lunch here at work and got a P0 300 code when moving the key to on several times but then each time after that I got "done" with no code. Is it normal for the code to show but then go to "done" ?

Thanks

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Unread 01-21-2014, 01:22 PM   #2
Cooneys08JK
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This has happened to me but my issue was different.

CELs stay on for 3 normal driving cycles. After that, if upon start up the issue remains, the code will reappear. If the problem cleared itself it would clear the code and go right to "done" when you do the key trick. My guess is you will see this CEL appear again in the near future...
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Unread 01-21-2014, 01:26 PM   #3
jhc09
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I should have explained it better but I only got the p0 300 code once in about 6 tries. Every try after the first p0 300 just said "done". It's as if the code cleared or something.
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Unread 01-21-2014, 01:27 PM   #4
Cooneys08JK
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Quote:
Originally Posted by jhc09 View Post
i should have explained it better but i only got the p0 300 code once in about 6 tries. Every try after the first p0 300 just said "done". It's as if the code cleared or something.
Yea I noticed that, and tried to edit my response...Whelp it may have been an issue on startup that has since fixed itself. Best thing to do is keep driving and see if it reappears. I wouldnt freak too much. You said the Jeep was idling rough? Is it sill? Even with no codes?
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Unread 01-21-2014, 01:29 PM   #5
jhc09
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I wanted to see the code a second time just to confirm what I was seeing.
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Unread 01-21-2014, 01:45 PM   #6
jhc09
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Quote:
Originally Posted by Cooneys08JK View Post
Yea I noticed that, and tried to edit my response...Whelp it may have been an issue on startup that has since fixed itself. Best thing to do is keep driving and see if it reappears. I wouldnt freak too much. You said the Jeep was idling rough? Is it sill? Even with no codes?
No more rough idling since that one time yesterday. I'll see how it goes. Thanks
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Unread 01-21-2014, 01:51 PM   #7
JeepCares
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Just some info from the factory service manual:

P0300-MULTIPLE CYLINDER MISFIRE

When Monitored:
Any time the engine is running, and the adaptive numerator has been successfully updated.

Set Condition:
The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes one soft fail to set a malfunction and two trips to set the MIL. Three good trips to turn off the MIL.

Possible Causes
(F342) ASD RELAY OUTPUT CIRCUIT
INJECTOR CONTROL CIRCUIT
COIL CONTROL CIRCUIT
IGNITION WIRE
SPARK PLUG
IGNITION COIL
FUEL PUMP INLET STRAINER PLUGGED
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP MODULE
FUEL PRESSURE LEAK DOWN
FUEL INJECTOR
ENGINE MECHANICAL
POWERTRAIN CONTROL MODULE (PCM)
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Unread 01-21-2014, 01:51 PM   #8
Cooneys08JK
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Quote:
Originally Posted by jhc09 View Post
No more rough idling since that one time yesterday. I'll see how it goes. Thanks
It seams like you caught most of the code. Here are the reasons for the P0300 codes...

P0300 ‐ Multiple Cylinder Misfire
P0301 ‐ Cylinder 1 Misfire
P0302 ‐ Cylinder 2 Misfire
P0303 ‐ Cylinder 3 Misfire
P0304 ‐ Cylinder 4 Misfire
P0305 ‐ Cylinder 5 Misfire
P0306 ‐ Cylinder 6 Misfire

Was this the first time you started the Jeep in a bit?? Just wondering because of your low miles...
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Unread 01-21-2014, 02:20 PM   #9
jhc09
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Quote:
Originally Posted by Cooneys08JK View Post
It seams like you caught most of the code. Here are the reasons for the P0300 codes...

P0300 ‐ Multiple Cylinder Misfire
P0301 ‐ Cylinder 1 Misfire
P0302 ‐ Cylinder 2 Misfire
P0303 ‐ Cylinder 3 Misfire
P0304 ‐ Cylinder 4 Misfire
P0305 ‐ Cylinder 5 Misfire
P0306 ‐ Cylinder 6 Misfire

Was this the first time you started the Jeep in a bit?? Just wondering because of your low miles...
It was not, I use it everyday.
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Unread 01-21-2014, 02:23 PM   #10
jhc09
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2009 JK Wrangler 
 
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Quote:
Originally Posted by JeepCares View Post
Just some info from the factory service manual:

P0300-MULTIPLE CYLINDER MISFIRE

When Monitored:
Any time the engine is running, and the adaptive numerator has been successfully updated.

Set Condition:
The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes one soft fail to set a malfunction and two trips to set the MIL. Three good trips to turn off the MIL.

Possible Causes
(F342) ASD RELAY OUTPUT CIRCUIT
INJECTOR CONTROL CIRCUIT
COIL CONTROL CIRCUIT
IGNITION WIRE
SPARK PLUG
IGNITION COIL
FUEL PUMP INLET STRAINER PLUGGED
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP MODULE
FUEL PRESSURE LEAK DOWN
FUEL INJECTOR
ENGINE MECHANICAL
POWERTRAIN CONTROL MODULE (PCM)
Thanks for the info. What are the recommendations for changing out plugs?
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Unread 01-21-2014, 03:08 PM   #11
duneslider
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I would hold off on changing plugs, they shouldn't be bad quite yet. Where it was P0300 and not indicating just one of the cylinders I would lean more to bad gas first. I would run it some more and see what happens. Maybe run some seafoam through the gas, or some other gas treatment (heet, etc.)
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Unread 01-21-2014, 09:05 PM   #12
jhc09
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The light went off after the 3 driving sessions you guys told me about. I will play the waiting game now and with some luck won't see it again. Thanks for the help.
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