P0351 on 2011-2015 Kia Optima 2.4L GDI: Ignition Coil 'A' Circuit Causes and Fixes

What's Unique About the 2011-2015 Kia Optima

The Theta II 2.4L GDI engine, used across the Hyundai/Kia lineup, is known for having ignition coils fail as a common wear item, often due to high heat in the engine bay. A frequent underlying cause on this specific engine is a leaking valve cover gasket, which allows oil to seep into the spark plug tubes. This oil saturates the coil boot and can short out the coil itself, leading to repeat failures if the gasket isn't replaced. While this engine is famous for a major recall related to engine bearing failure, the P0351 code is typically a separate, more straightforward ignition system problem.

Symptoms You May Notice

• Check Engine Light is on (may flash if misfire is severe)
• Rough engine idle or shaking
• Engine sputtering or hesitating during acceleration
• Noticeable loss of power
• Reduced fuel economy
• Difficulty starting the engine

Most Likely Causes

1. Failed Ignition Coil on Cylinder #1 🔴 High Probability → Shop Ignition Coil Ignition coils on the Theta II GDI engine are a very common failure point due to high heat exposure and age-related breakdown of internal windings.
   How to confirm: Perform a 'coil swap test'. Move the ignition coil from cylinder #1 (leftmost) to cylinder #2 using a 10mm socket or wrench. Clear the codes. If the fault code changes to P0352, the coil is definitively bad.
   Typical fix: Replace the faulty ignition coil. 🎬 Watch: How to replace the spark plugs and coil packs
   Est. part cost: $25-$75
2. Leaking Valve Cover Gasket / Spark Plug Tube Seals 🟡 Medium Probability → Shop Engine Valve Cover The gasket and tube seals on the 2.4L GDI engine are known to become brittle from heat cycles, allowing oil to leak into the spark plug wells. This oil saturates and destroys the ignition coil boot, causing a misfire.
   How to confirm: When you remove the ignition coil for cylinder #1, visually inspect the spark plug well and the coil's rubber boot for liquid engine oil. A Reddit user confirmed this exact issue on their 2013 Optima Hybrid.
   Typical fix: Replace the valve cover gasket and the spark plug tube seals. 🎬 See this step-by-step valve cover gasket replacement guide Clean all oil out of the spark plug well before installing the new coil and plug.
   Est. part cost: $20-$50
3. Worn or Fouled Spark Plug in Cylinder #1 🟡 Medium Probability → Shop Spark Plug GDI engines are sensitive to spark plug condition. An old plug with a wide gap or one fouled by oil (from a leaking gasket) or carbon (from GDI deposits) can strain the ignition coil, leading to its premature failure.
   How to confirm: After removing the ignition coil, remove and inspect the spark plug. Look for heavy carbon deposits, oil fouling, or a worn-down electrode.
   Typical fix: Replace the spark plug. It is best practice 🎬 Watch: 2.4L GDI spark plug replacement walkthrough to replace all four spark plugs as a set if they are near their service interval.
   Est. part cost: $10-$20
4. Damaged Wiring or Electrical Connector ⚪ Low Probability Engine heat and vibration can make the plastic locking tab on the coil's electrical connector brittle, leading to a poor connection. Rodents are also known to chew on engine bay wiring.
   How to confirm: Visually inspect the wiring harness and the connector for cylinder #1. Check for cracks, corrosion, or broken wires. Wiggle the connector with the engine running to see if it affects the idle, indicating a loose connection.
   Typical fix: Repair the damaged wire or replace the pigtail connector. Pigtail connectors are readily available online.
   Est. part cost: $10-$25

Rare But Worth Checking

• Failed Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is extremely rare. The PCM's internal driver for the ignition coil can fail, but every other possibility should be exhausted before considering PCM replacement. This is a last resort after confirming the coil, plug, and wiring are all good.

Diagnosis Steps

1. Scan the vehicle for all DTCs. Note P0351 and any other codes like P0301.
2. Turn off the engine and locate cylinder #1. On the 2.4L GDI, it is the cylinder on the far left (driver's side) when facing the engine.
3. Disconnect the electrical connector from the cylinder #1 and cylinder #2 ignition coils. Remove the 10mm bolt holding each coil in place.
4. Swap the ignition coil from cylinder #1 with the coil from cylinder #2.
5. Reinstall the bolts and reconnect the electrical connectors.
6. Clear the diagnostic codes with your scanner.
7. Start the engine and let it run for a minute. Re-scan for codes.
8. If code P0352 ('Ignition Coil 'B' Circuit Malfunction') appears, the ignition coil you moved is faulty and must be replaced.
9. If code P0351 returns, the coil is good. The problem lies in the wiring or spark plug for cylinder #1.
10. Remove the coil from cylinder #1 again. Using a flashlight, inspect the spark plug well for any signs of liquid oil. If oil is present, the valve cover gasket is leaking and must be replaced to prevent future coil failures.
11. If no oil is present, remove the spark plug from cylinder #1. Inspect it for excessive wear, cracks, or fouling. Replace if necessary.
12. If the plug is good, carefully inspect the electrical connector and wiring going to the cylinder #1 coil for any damage, corrosion, or loose pins. Ensure the locking tab on the connector is not broken.

Parts You'll Likely Need

• Ignition Coil (OEM #27300-3F100 (supersedes 27300-2G000)) — This is the most common failure part for code P0351 on this engine. Part number 27300-3F100 is the updated OEM replacement for the original 27300-2G000.
  Trusted brands: Hyundai/Kia (OEM), NGK, Delphi, Denso
  OEM price range: $60-$90
  Aftermarket price range: $25-$75
• Iridium Spark Plug (OEM #NGK SILZKR7B11 or Denso FXU16HR11) — Often replaced alongside the ignition coil as a set, or if it is found to be fouled or worn, which can cause the code.
  Trusted brands: NGK, Denso
  OEM price range: $15-$25
  Aftermarket price range: $10-$20
• Valve Cover Gasket Kit (OEM #22441-2G670 (For US-built Optimas) or 22441-2G710 (For Korea-built Optimas)) — Required if oil is found in the spark plug well, as this is a common root cause of the coil failure. The part number depends on the vehicle's country of manufacture.
  Trusted brands: Hyundai/Kia (OEM), Fel-Pro, Mahle
  OEM price range: $40-$60
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0301 — P0301 means 'Cylinder 1 Misfire Detected'. A fault in the ignition coil circuit (P0351) is a direct cause for a lack of spark, which results in a misfire on that cylinder. This code is almost always present with P0351.
• P0352, P0353, P0354 — These codes indicate the same fault on other cylinders. If you get multiple coil codes at once, it could point to a shared power/ground issue, a major wiring harness problem, or a failing PCM, rather than multiple coils failing simultaneously.

Technical Service Bulletins (TSBs) & Recalls

• TSB CHA072 / CS1604: While not directly related to P0351, this TSB addresses the common steering coupler failure on 2011-2014 Optimas, which is a key platform issue owners should be aware of.

Platform-Specific Known Issues

• Real Owner Experience: On optimaforums.com, a user with a 2011 Optima EX reported a flashing check engine light and codes P0301 and P0351. After swapping the coil from cylinder 1 to 2, the codes changed to P0302 and P0352, confirming a bad coil. The user replaced the single coil and the problem was resolved. This is a classic example of the coil swap test working perfectly.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: 0.45 - 0.65 ohms. Failure: A reading of 0 ohms indicates a short, while a significantly higher or infinite reading (OL) indicates an open circuit.
• Ignition Coil Secondary Winding Resistance — expected: 6,000 - 10,000 ohms (6kΩ - 10kΩ). Failure: Readings outside this range suggest the coil's internal secondary winding is faulty and the coil should be replaced.
• PCM Ignition Driver Signal at Coil Connector — expected: 5 - 20 Hz with engine running. Failure: A reading of 0 Hz indicates the PCM is not sending a trigger signal. This points to a wiring issue or a failed PCM driver, not a bad coil.

Wiring & Ground Locations

• Engine Ground Strap (US-built) — Connects the engine block to the vehicle chassis to ensure a good electrical ground path.. A corroded or loose main engine ground can cause intermittent and strange electrical issues, including ignition system faults. The specific part number for 2012-2013 US-built Optimas with the 2.4L engine is 91860-4C010.
• Engine Ground Strap (Korea-built) — Connects the engine block to the vehicle chassis to ensure a good electrical ground path.. A poor ground connection can affect the ignition system's performance. The part number for 2011-2013 Korea-built Optimas with the 2.4L engine is 91860-2T011.

OEM Part Supersession History

• 27300-2G000 → 27300-3F100, 27300-2GGA0 — OEM parts are often superseded to improve reliability, thermal management, or manufacturing efficiency. The newer part numbers are the correct service replacements.
  Heads up: While visually similar, coils for the 2.0L Turbo engine have different electrical characteristics and connector pinouts and must not be used on the 2.4L engine.

Model Year Variations Within This Range

• 2011-2015: The correct part number for the main engine ground strap depends on whether the vehicle was built in the US (Part No. 91860-4C010 for '12-'13) or Korea (Part No. 91860-2T011 for '11-'13). This can be determined by the first character of the VIN ('5' for US, 'K' for Korea).

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Catastrophic Engine Failure (Rod Bearing Failure) 🔴 High — Extremely common across the entire 2011-2019 model year range. A class-action lawsuit resulted in a lifetime warranty for the engine short block for many owners. (Ref: NHTSA Recalls 20V750, 20V751, 21V077; Safety Recall Campaign SC147.)
• Intake Valve Carbon Buildup 🟠 Medium — Common on GDI engines, typically becoming noticeable between 60,000 and 100,000 miles. Leads to rough idle, misfires (P030x), and power loss.
• Degrading Steering Coupler 🟠 Medium — Very common; the flexible rubber coupler in the electronic power steering column wears out, causing a distinct clicking or clunking noise when turning the wheel. (Ref: Customer Satisfaction Program CS1604 / TSB CHA072 extended the warranty to 10 years/unlimited miles for this part.)
• Excessive Oil Consumption 🔴 High — Often a precursor to rod bearing failure, this issue is caused by carbon buildup on oil control rings. Many owners report needing to add oil between changes. (Ref: Related to the engine failure class action settlement.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, a used engine wiring harness is a smart choice if the original is damaged by rodents or heat, as a new harness is very expensive. A used valve cover is also acceptable if sourced from a low-mileage vehicle and inspected for cracks or warping.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a wiring harness, inspect for any signs of brittle insulation, previous repairs (tape, butt connectors), or rodent damage.
• For a valve cover, ensure it is perfectly flat by placing it on a known flat surface and check for any cracks, especially around bolt holes.

OEM-only on this vehicle (don't cheap out):

• Powertrain Control Module (PCM) - Aftermarket or improperly matched used units can have VIN lock or software compatibility issues. It's best to use an OEM unit or a specialist remanufacturing service.
• Valve Cover Gasket - Some owners report that aftermarket gaskets like Fel-Pro can be difficult to install as they may not fit snugly in the valve cover's groove and can fall out during installation. The OEM gasket is often preferred for a perfect fit.

Aftermarket brands forum-validated for this vehicle:

• Ignition Coils: NGK, Delphi, Denso, and Mando (an OE supplier for Kia/Hyundai) are widely regarded as reliable alternatives to the dealer part.

Brands owners have reported issues with on this vehicle:

• Ultra-cheap, no-name ignition coils from online marketplaces are a gamble and frequently cited in forums as failing prematurely.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0301 — Cylinder 1 Misfire Detected; frequently appears with P0351 when the ignition coil or spark plug in the first cylinder fails.
• P0352 — Ignition Coil 'B' Circuit Malfunction; this code will appear during a 'coil swap test' if the faulty coil from cylinder 1 is moved to cylinder 2.
• P0302 — Cylinder 2 Misfire Detected; often follows a P0351 diagnosis during troubleshooting if the suspected coil is moved to the second cylinder.
• P030X — General misfire codes that can be triggered by carbon buildup on intake valves, a common issue for the Theta II GDI engine.

Frequently Asked Questions