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Code P0303 (Ignition systems) & Code C1201/51 (Engine control system)

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Code P0303 (Ignition systems) & Code C1201/51 (Engine control system)

Old 10-19-2017, 09:28 PM
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Default Code P0303 (Ignition systems) & Code C1201/51 (Engine control system)

My 2011 xD threw the following codes this AM at ~133,233 miles:

Code P0303 (ignition systems)
Code C1201/51 (engine control system)

The symptom -- minor surging when under load, as well as when stopped) -- began yesterday.

Plugs and coils were replaced at 124,688 and the vehicle has been running nominally until now.

Code P0303 points to ignition coils, spark plugs and intake manifold gasket. I believe that cylinder 3 is potentially the culprit. (Is that the 2nd coil on the left or right when facing the engine bay?)

Code C1201/51 refers to an engine control system malfunction signal which continues for 1 second or more.

Please let me know if you can shed any additional code definitions and/or any ideas regarding where to start troubleshooting after the #3 coil is checked?

Cheers!

Last edited by MR_LUV; 10-20-2017 at 01:44 AM. Reason: Approved Post
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Old 10-21-2017, 12:02 AM
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Most engines number the cylinders from the driver side and front to back.
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Old 10-21-2017, 01:06 PM
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Originally Posted by DAlex View Post
Most engines number the cylinders from the driver side and front to back.
Thanks for the feedback!

I'm going to switch the coil from cylinder #3 with #4 and see if the code changes.

If that does not occur, I will switch the plug from cylinder #3 with #1 and see if the code changes.

If that does not occur, perhaps the suspect is a stuck fuel injector in #3...

More shall be revealed later today...
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Old 10-22-2017, 04:18 PM
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OK, if you had accidentally mis-attached coils, your engine would've been running like a washing machine with a bowling ball in it. A mis-wired 4 cylinder is NOT subtle; Harley Davidsons idle smoother! If a coil had been mis-attached, your motor would make loud backfires, and would idle rough enough to be heard from 1000' away. Your recurring rough idle is much less severe.
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Old 10-22-2017, 06:21 PM
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To complete the loop:

The practically new (Denso Iridium) plug with ~7,500 miles that was in cylinder #3 was bad.

To troubleshoot I moved it to cylinder #2 and sure enough code P0302 was recorded. I purchased a Bosch Iridium plug at O'Reilly's and installed it and all is well...fingers crossed...
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Old 10-22-2017, 06:22 PM
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Originally Posted by DAlex View Post
OK, if you had accidentally mis-attached coils, your engine would've been running like a washing machine with a bowling ball in it. A mis-wired 4 cylinder is NOT subtle; Harley Davidsons idle smoother! If a coil had been mis-attached, your motor would make loud backfires, and would idle rough enough to be heard from 1000' away. Your recurring rough idle is much less severe.
Thanks for the feedback. I'll keep this in mind if something transpires again...
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