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P0356 on 2012-2018 Jeep Wrangler: Ignition Coil F (Cylinder 6) Failure Causes and Fixes

P0356 on a 3.6L Pentastar V6 Jeep Wrangler indicates a fault with the ignition coil circuit for cylinder #6. The most common cause is a failed ignition coil, which is a straightforward DIY fix once the intake manifold is removed. Swapping the coil with an adjacent one is the easiest way to confirm the diagnosis before buying parts.

21 minutes to read 2012-2018 Jeep Wrangler

Most Likely Cause

Failed Ignition Coil (Cylinder 6)

Difficulty

3/5

Est. Time

2 hrs

DIY Doable?

✅ Yes

Shop Labor

$250 – $550

Parts Price

$30 – $150

⚠️ Drivable, but... — Driving with an active P0356 code means you have a constant engine misfire on one cylinder. This can cause unburned fuel to enter the exhaust and damage the catalytic converter, leading to a very expensive repair. It is best to fix it as soon as possible and avoid heavy acceleration. If the Check Engine Light is flashing, you should pull over and stop driving to prevent certain damage.

Key Takeaways

P0356 specifically points to an electrical fault in the ignition coil circuit for cylinder #6.
The most likely culprit is a failed ignition coil, which is a common issue on the 3.6L Pentastar engine.
A definitive diagnosis can be made by swapping the cylinder #6 coil with another one and seeing if the trouble code follows the coil.
Accessing cylinder #6 requires removing the upper intake manifold, so it is strongly recommended to replace all three driver's side spark plugs and the intake gaskets at the same time to avoid duplicate labor in the future.
Do not drive for an extended period with this code, as the resulting misfire can cause expensive damage to the catalytic converter.

The trouble code P0356 stands for "Ignition Coil 'F' Primary/Secondary Circuit Malfunction." The letter 'F' corresponds to the engine's sixth cylinder. This means the Powertrain Control Module (PCM) has detected an electrical problem in the ignition coil circuit for cylinder #6. The PCM monitors the voltage feedback from the coil's primary circuit after commanding it to fire; if this feedback signal is missing or incorrect, it assumes a fault, sets this code, and illuminates the Check Engine Light.

What's Unique About the 2012-2018 Jeep Wrangler

The 3.6L Pentastar V6 is a very common engine across many Jeep, Dodge, and Chrysler vehicles. On the Jeep Wrangler JK, this code is a frequent issue, often due to a simple coil failure. The main platform-specific challenge is access. Cylinder #6 is located on the driver's side of the engine, towards the rear (closest to the firewall). Replacing this coil requires removing the upper intake manifold, making the job more time-consuming than for the passenger-side cylinders. This procedure is common across all vehicles with the 3.6L Pentastar in a longitudinal (RWD-based) layout.

Symptoms You May Notice

Engine misfire (shaking, stumbling, or rough running)
Flashing or solid Check Engine Light
Reduced engine power and poor acceleration
Rough idle
Decreased fuel economy
Hard start or no-start condition in some cases

⚠️ Don't Waste Money on the Wrong Fix

Replacing only the spark plug without testing the ignition coil.
Replacing the PCM before thoroughly testing the coil and wiring.
Assuming a P0306 (Cylinder 6 Misfire) is a fuel injector issue when P0356 is also present. The P0356 circuit code is the root cause and should be diagnosed first.

Most Likely Causes

Failed Ignition Coil (Cylinder 6) 🔴 High Probability Ignition coils are wear items that operate in a high-heat, high-vibration environment. The coil for cylinder #6 on the Pentastar is a common failure point due to its location and the general failure rate of coils on this engine.
How to confirm: The easiest method is to swap the ignition coil from cylinder #6 with another cylinder (e.g., cylinder #4, which is also on the driver's side). Clear the codes and run the engine. If the code changes to P0354, the coil is confirmed to be faulty.
Typical fix: Replace the faulty ignition coil. 🎬 See this step-by-step ignition coil replacement guide It is often recommended to replace all three coils on the driver's side bank while the intake manifold is removed to save on future labor.
Est. part cost: $25-$75
Worn or Fouled Spark Plug (Cylinder 6) 🟡 Medium Probability A worn spark plug with an excessive gap forces the ignition coil to work harder, which can lead to premature coil failure and trigger a circuit code. Since replacing the coil on cylinder #6 requires removing the intake manifold, it's highly recommended to replace the spark plugs at the same time, especially if they are near their service interval (typically 100,000 miles).
How to confirm: After removing the ignition coil, remove the spark plug and inspect it for wear, carbon buildup, oil fouling, or damage to the electrode or insulator. A cracked ceramic insulator is a known issue.
Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs at the same time, or at minimum the three on the driver's side bank.
Est. part cost: $5-$15 per plug
Damaged Wiring or Loose Connector ⚪ Low Probability Engine vibrations and heat can cause wires to chafe or the plastic locking tab on the coil's electrical connector to become brittle and break. A broken tab can lead to a poor connection that vibrates loose. Some owners report successfully securing a loose connector with a zip tie as a temporary or permanent fix.
How to confirm: Visually inspect the wiring harness leading to the cylinder #6 ignition coil for any signs of abrasion, melting, or breaks. Check that the connector is fully seated and the locking tab is engaged. Wiggle the connector with the engine running (if accessible and safe) to see if it induces a misfire.
Typical fix: Repair the damaged section of wiring or replace the connector pigtail. If only the lock tab is broken, a zip tie can be used to secure the connection.
Est. part cost: $10-$30

Rare But Worth Checking

Failed Powertrain Control Module (PCM): This is the least likely cause. The internal driver circuit in the PCM that controls the ignition coil can fail. This should only be considered after all other possibilities (coil, plug, wiring) have been definitively ruled out using a multimeter to test the circuit. Replacing a PCM requires programming it to the vehicle's VIN.
Oil/Coolant Contamination in Wiring Harness: The 3.6L Pentastar is notorious for its plastic oil filter/cooler housing, which sits in the 'V' of the engine and is prone to cracking and leaking oil and/or coolant into the valley. This fluid can saturate wiring harnesses that run underneath, including ignition and sensor wiring, potentially causing shorts or open circuits that could trigger a P0356 code.

Diagnosis Steps

Verify the presence of the P0356 code (and any others like P0306) using an OBD-II scanner.
Identify cylinder #6. On the 3.6L Pentastar V6 in a RWD layout like the Wrangler, the cylinders on the driver's side (left bank) are 2, 4, and 6, from front to back. Cylinder #6 is the one closest to the driver's firewall.
To access the driver's side coils, you must remove the upper intake manifold. 🎬 Watch: How to remove the Pentastar intake manifold This involves disconnecting the air intake tube, several sensors, vacuum hoses, and unbolting the manifold itself. Place shop towels in the open lower intake ports to prevent debris from falling into the engine.
Once the intake is removed, swap the ignition coil from cylinder #6 with the coil from cylinder #4.
While the intake is off, it is highly advisable to replace all three spark plugs on this bank (2, 4, 6) and the upper/lower intake manifold gaskets, as they are one-time use.
Reassemble the intake manifold, clear the diagnostic codes, and start the engine. Let it run for a few minutes.
Re-scan for codes. If the code has changed to P0354 ("Ignition Coil D Circuit Malfunction"), the ignition coil you moved is faulty and needs to be replaced.
If the P0356 code returns, the problem is not the coil. The next step is to inspect the wiring connector for cylinder #6 for pushed-out pins, corrosion, or damage. Use a multimeter to verify 12V power and the pulsing ground signal from the PCM at the connector.
If the coil, plug, and wiring all appear to be in good condition, the issue may be with the PCM, which requires professional diagnosis.

Parts You'll Likely Need

Ignition Coil (OEM #5149168AJ) — This is the most common cause of a P0356 code. The original part number 5149168AH has been superseded by 5149168AJ.
Trusted brands: Mopar, NGK, Denso
OEM price range: $45-$70
Aftermarket price range: $25-$50
Spark Plug (OEM #SP149125AD) — It is highly recommended to replace the spark plugs, especially on the difficult-to-access driver's side, whenever the intake manifold is removed for a coil replacement.
Trusted brands: Champion, NGK
OEM price range: $10-$20
Aftermarket price range: $5-$15
Upper and Lower Intake Manifold Gaskets (OEM #Upper: 5184331AC, Lower: 5184562AC. Often sold in kits.) — These gaskets are one-time use and must be replaced anytime the intake manifold is removed to prevent vacuum leaks. They are often sold as a set. Aftermarket kits like Fel-Pro MS97204 are also available.
Trusted brands: Mopar, Fel-Pro
OEM price range: $30-$50
Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

P0306 — P0306 means "Cylinder 6 Misfire Detected." Since a faulty ignition coil circuit (P0356) prevents a proper spark, it will almost always cause a misfire on that same cylinder. P0356 is the cause, P0306 is the effect.

Technical Service Bulletins (TSBs) & Recalls

TSB 09-013-20 REV. A: While not directly for P0356, this TSB addresses misfire codes (P030x) on 2020-2021 models with the 3.6L engine due to internally cracked spark plugs, highlighting a known issue with ignition components on the Pentastar.

Platform-Specific Known Issues

In early 2012 models, a P0306 misfire code was sometimes an early symptom of a larger cylinder head problem that was covered under an extended warranty by Chrysler. While P0356 is an electrical code, it's worth noting this historical context for early model year vehicles.
The plastic locking tab on the ignition coil connector is known to become brittle and break, leading to a loose connection. This is a common point of failure for the circuit.

Mechanic-Grade Diagnostic Values

Ignition Coil Primary Winding Resistance — expected: 0.62 Ohms ± 10% at 68°F (20°C). Failure: A reading significantly higher than the specification, or an open circuit (infinite resistance). Note: This low resistance is difficult to measure accurately with many standard multimeters.
Ignition Coil Secondary Winding Resistance — expected: 7.0k Ohms ± 15% at 68°F (20°C). Failure: A reading outside of the 6,000 to 15,000 Ohm range often indicates a faulty coil. An open or shorted reading confirms failure.
Coil Connector Pin 1 Voltage (Power Supply) — expected: Battery voltage (approx. 12V) with ignition on. This is the ASD (Auto Shutdown) relay output.. Failure: No voltage indicates an open circuit in the power supply from the ASD relay or a blown fuse.
Coil Connector Pin 2 Signal (PCM Control) — expected: Pulsing ground signal when the engine is cranking or running. This is best observed with an oscilloscope or a test light connected to 12V.. Failure: A steady ground, steady voltage, or no signal indicates a problem with the wiring to the PCM or the PCM's internal driver circuit.

Scan Tool Commands That Help

wiTECH or equivalent professional scanner: Actuate Main/ASD Relay — When testing the power supply circuit (Pin 1) at the ignition coil connector. This command forces the relay on, allowing you to check for battery voltage at the coil without needing the engine to run.

Wiring & Ground Locations

Cylinder 6 Coil Connector — On the ignition coil for the rearmost cylinder on the driver's side of the engine, under the upper intake manifold.. This is the primary connection point for testing. Pin 1 is the power feed from the ASD relay, and Pin 2 is the ground control signal from the PCM. A poor connection here is a common cause of P0356.
PCM (Powertrain Control Module) — In the engine bay, typically on the firewall or inner fender.. The PCM provides the switched ground signal to Pin 2 of the coil connector to fire the coil. A failure of the internal driver circuit for cylinder 6 within the PCM will cause P0356 and requires PCM replacement.

Real Owner Repair Stories

Jeep Wrangler JK Forum User (2015 Jeep JKU Rubicon 3.6L) — Intermittent P0306 code for months, occasional pulsing sensation when letting off the gas in traffic.
❌ Tried (didn't work) Replacing all ignition coils and spark plugs., Replacing the PCV valve., Dealer performed a software update., Dealer replaced cylinder head(s) under warranty after a leak-down test showed poor exhaust valve sealing.
✅ What actually fixed it The user's issue persisted after multiple dealer visits and major part replacements. While the final post is unresolved, the extensive list of failed fixes points towards a more elusive cause like an intermittent wiring issue or a faulty PCM, which the user suspected but the dealer had not yet replaced.
YouTube Channel '3.6L oil in the wiring' (Jeep with 3.6L Pentastar) — Boggy power, stalling, multiple codes after an oil cooler leak.
❌ Tried (didn't work) Replacing the leaking oil cooler but attempting to clean and reuse the oil-saturated wiring harnesses.
✅ What actually fixed it The oil had wicked through the wiring insulation, causing persistent shorts and bad connections. The final fix required replacing all three affected engine wiring harnesses (main harness, injector sub-harness, and oil cooler sub-harness) because cleaning was not effective.

OEM Part Supersession History

5149168AH, 5149168AI → 5149168AJ — Standard part revision and improvement by the manufacturer.

Model Year Variations Within This Range

2012-2013: Early 3.6L Pentastar engines had a higher incidence of left-side cylinder head failures, leading to an extended warranty (X69). While this typically sets a P030X misfire code, the underlying mechanical issue could potentially contribute to or be misdiagnosed alongside an electrical code like P0356.
2012: The 3.6L Pentastar V6 engine and five-speed automatic transmission were introduced, representing a major powertrain upgrade from the previous 3.8L V6 and four-speed automatic.

Diagnostic Flowchart

P0356 indicates a circuit malfunction for the Cylinder #6 ignition coil. Because Cylinder #6 is located at the driver-side rear (near the firewall) under the intake manifold, diagnosis requires a systematic approach to avoid unnecessary labor.

Inspect the Cylinder #6 coil connector (driver's side, closest to firewall). Is the plastic locking tab broken or the connector loose?

→ The Pentastar engine's heat often makes these tabs brittle. Secure the connector with a zip tie or replace the pigtail connector ($10-$30) to ensure a solid electrical connection.

Remove the upper intake manifold to access Cylinder #6. Swap the #6 coil with the #4 coil. Clear codes and restart. Does the code change to P0354?

The coil is faulty. While the intake is off, what is the condition of the spark plugs?

→ Replace the faulty coil ($25-$75). It is highly recommended to replace all 6 spark plugs and the upper intake manifold gaskets now to prevent future labor, as noted in Pentastar service best practices.

→ Replace only the failed Cylinder #6 ignition coil and reassemble using new intake manifold gaskets.

With the coil ruled out, use a multimeter at the #6 connector. Is there 12V power and a pulsing ground signal from the PCM?

→ Trace the circuit back to the PCM. If the wiring has continuity but no signal, the PCM driver may have failed, requiring professional replacement/reprogramming.

If electrical tests pass but P0356/P0306 persists, do you hear a 'ticking' noise from the driver-side valve cover?

→ This may be a failed rocker arm or needle bearing, a common Pentastar V6 issue. Inspect the camshaft lobes and rockers on the left bank for wear.

→ Perform a compression and leak-down test on Cylinder #6. On 2012-2013 models, be aware of the known left-bank cylinder head failure issue which can mimic ignition symptoms.

Visually inspect the wiring harness leading to the driver-side bank. Any signs of rodent damage or chafing against the fuel rail/valve cover?

→ Repair the damaged wiring section. If the harness is melted, check for nearby exhaust leaks or overheating issues.