Check engine light turned on with code P0306

Hi,

Chances are you have a spark plug wire or spark plug needing replaced. Here are directions for checking the condition of the wires and spark plugs:

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2003 Hyundai Sonata V6-2.7L
Inspection and Cleaning
Vehicle Powertrain Management Ignition System Ignition Cable Service and Repair Procedures Inspection and Cleaning
INSPECTION AND CLEANING
1. Disconnect the spark plug cable from the spark plug.

NOTE: Pull on the spark plug cable boot when removing the sparkplug cable, not the cable, as it may be damaged.

pic 1

2. Using spark plug wrench, remove all of the spark plugs from the cylinder head.

NOTE: Take care not to allow contaminants to enter through the spark plug holes.

pic 2

3. Check spark plugs for the following:
1. Broken insulator
2. Worn electrode
3. Carbon deposits
4. Damaged or broken gasket
5. Condition of the porcelain insulator at the tip of the spark plug

pic 3

4. Check the spark plug gap using a wire gap gauge, and adjust if necessary.

Standard value
Spark plug gap: 1.0 - 1.1 mm (0.039 - 0.043 in.)

5. Re-insert the spark plug and tighten to the specified torque. If it is overtorqued, damaged to the threaded portion of cylinder head may result.

Tightening torque
Spark plug: 20 - 30 Nm (204 - 306 kg.cm, 15 - 21 lb.ft)

NOTE: When replacing spark plugs, use any equivalent resistance type spark plugs.

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Here are the spark plug wiring routing directions.

2003 Hyundai Sonata V6-2.7L
Installation of Spark Plug Cable
Vehicle Powertrain Management Ignition System Ignition Cable Service and Repair Procedures Installation of Spark Plug Cable
INSTALLATION OF SPARK PLUG CABLE

pic 4

Improper arrangement of spark plug cables will induce voltage between the cables, causing misfiring and surging at acceleration in high-speed operation.

Therefore, be careful to arrange the spark plug cables properly as shown in the illustration.

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Here is a link that shows in general how a tune up is performed.

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

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Now there are other things that can cause a misfire such as fuel pressure, low compression, timing issues and so on. However, since you only have the one code, this is where I would start. If you haven't tuned it up in a long time, it would be a good preventative maintenance thing to do.

Let me know if this helps or if you have other questions.

Joe