P0356 is an ignition coil circuit trouble code that can cause misfires, rough running, and even stalling if you ignore it. This code points to a problem with the ignition coil circuit on cylinder 6, but the root cause can be anything from a bad coil to damaged wiring or even an ECU fault. In this guide, you’ll learn what P0356 means in plain language, the most common symptoms and causes, how a mechanic actually diagnoses it, and what repairs and costs you should realistically expect.
What Does P0356 Mean?
P0356 is an OBD-II diagnostic trouble code that stands for “Ignition Coil F Primary/Secondary Circuit Malfunction.” In simple terms, your engine computer (ECU/PCM) has detected an electrical problem in the ignition coil circuit for cylinder 6.
The ECU constantly monitors the voltage and current going to each coil. When it sees a signal that’s out of range (open circuit, short to power, short to ground, or erratic), it sets P0356 and usually turns on the check engine light. On many vehicles, the ECU will also disable fuel injection to that cylinder to protect the catalytic converter.
Quick Reference
- Code: P0356
- Meaning: Ignition Coil F (Cylinder 6) Circuit Malfunction
- Type: Ignition / electrical fault
- Severity: Moderate to high (can damage catalytic converter if ignored)
- Typical fixes: Replace coil, repair wiring/connector, occasionally ECU repair
Real-World Example / Field Notes
In the shop, I see P0356 a lot on V6 engines where each cylinder has its own coil-on-plug setup. A typical case: customer comes in with a flashing check engine light, rough idle, and a strong fuel smell. Scan tool shows P0356 and a misfire on cylinder 6. Swapping the cylinder 6 coil with another cylinder moves the misfire and sets a new code for that cylinder. That confirms a bad coil. Other times, especially on older or high-mileage vehicles, I’ll find a cracked coil connector or brittle wiring right at the coil, causing an intermittent open circuit that only shows up when the engine is hot or vibrating.
Symptoms of P0356
- Check engine light on: Often steady, but may flash under heavy load when misfire is severe.
- Rough idle: Engine shakes or feels uneven, especially at stoplights or in park.
- Loss of power: Noticeable lack of acceleration, especially when climbing hills or passing.
- Engine misfire: Stumbling, hesitation, or jerking during acceleration or cruising.
- Poor fuel economy: You burn more fuel because one cylinder isn’t contributing properly.
- Fuel smell from exhaust: Unburned fuel can cause a strong odor and possible backfiring.
- Hard starting or no start: In some cases, especially if multiple coil circuits are affected.
- Possible catalytic converter damage: Long-term misfires can overheat and melt the converter.
Common Causes of P0356
Most Common Causes
- Failed ignition coil on cylinder 6: Internal coil windings break down, causing weak or no spark and abnormal current draw that the ECU detects.
- Damaged coil connector: Loose, corroded, or broken terminals at the cylinder 6 coil plug cause intermittent or open circuit conditions.
- Wiring harness issues: Chafed, pinched, or broken wires between the ECU and the coil (power, ground, or control wire) create open circuits or shorts.
- Oil or moisture intrusion: Valve cover gasket leaks or water intrusion around the coil can cause corrosion and shorting at the coil or connector.
- Aftermarket coil quality problems: Cheap replacement coils sometimes fail early or have incorrect resistance, triggering circuit codes.
Less Common Causes
- ECU/PCM driver failure: The internal transistor (driver) that controls cylinder 6’s coil can fail, causing no signal or a stuck-on condition.
- Incorrect spark plugs or gap: Wrong plug type or excessive gap can overload the coil and eventually cause circuit faults.
- Previous engine work damage: Harness pulled too hard, connectors not fully seated, or wires pinched after intake manifold or valve cover work.
- Rodent damage: Mice or rats chewing on the ignition harness near the firewall or valve cover area.
- Internal short inside the coil boot: Carbon tracking down the boot to the plug can alter coil current and trigger the code.
Diagnosis: Step-by-Step Guide
To diagnose P0356 properly, you’ll want a basic OBD-II scan tool, a digital multimeter, and ideally access to wiring diagrams for your vehicle. A lab scope is helpful for pros, but you can get pretty far with just a meter and some careful testing. Always work on a cool engine and disconnect the battery when probing connectors to avoid shorts.
- Confirm the code and check for companions. Scan for codes and note any related misfire codes (like P0306) or other coil circuit codes. Clear the codes, then run the engine to see what returns.
- Perform a visual inspection. Locate cylinder 6 (check your firing order and bank layout) and inspect the coil, connector, and harness. Look for cracks, burn marks, oil in the plug well, or broken wires.
- Swap coils between cylinders. Move the cylinder 6 coil to another cylinder and move that coil to cylinder 6. Clear codes and test drive. If the code follows the coil to the new cylinder, the coil is bad.
- Check power and ground at the coil. With the key on (engine off), use a multimeter to verify 12V power and a good ground at the coil connector. Compare readings to a known-good cylinder if needed.
- Test the coil control signal. With the engine cranking or running, use a test light or scope (if available) on the coil control wire. You should see a pulsed signal. No pulse suggests a wiring or ECU driver issue.
- Inspect wiring continuity. With the battery disconnected, measure resistance between the coil connector and the ECU pin for the control wire. High resistance or open circuit means a break in the harness.
- Check for shorts to ground or power. With the coil unplugged, verify the control wire isn’t shorted to ground or battery voltage by checking resistance to ground and to the 12V feed.
- Review Mode $06 data (if available). Some scan tools let you see misfire counters and coil performance. This can confirm whether cylinder 6 is consistently misfiring versus intermittent.
- Evaluate ECU only after everything else checks out. If the coil, wiring, power, and ground are all good, but there’s still no control signal, the ECU driver for cylinder 6 may be faulty and require professional testing or replacement.
Pro tip: Don’t just throw a coil at it because P0356 mentions the coil circuit. Spend a few minutes inspecting and wiggling the harness with the engine running. If the engine stumbles when you move the wiring, you’ve likely found a wiring or connector issue, not a bad coil.
Possible Fixes & Repair Costs
The correct repair depends on what you find during diagnosis, but most P0356 fixes are straightforward. Typical repairs include replacing the cylinder 6 ignition coil, repairing or replacing damaged wiring or connectors, and occasionally replacing spark plugs or the ECU if the driver is bad. In general, you can expect repair costs to range from about $100–$250 for a single coil replacement up to $600–$1,200 or more if wiring harness sections or the ECU need repair. Labor rates, parts quality (OEM vs aftermarket), engine layout, and how hard the coil is to access all affect the final cost.
- Replace cylinder 6 ignition coil: Most common fix; often done along with a new spark plug. Parts and labor usually $100–$300 depending on vehicle.
- Replace all coils (preventive on high-mileage engines): Some owners choose to replace all coils at once, especially on older V6 engines, which can run $400–$900+.
- Repair or replace coil connector: New pigtail connector and solder/heat-shrink repair typically $120–$250.
- Repair wiring harness: Fixing chafed or broken wires can range from $150–$400 depending on access and length of harness affected.
- ECU/PCM replacement or repair: Least common but most expensive; expect $500–$1,500 including programming if the coil driver is confirmed failed.
- Replace spark plug on cylinder 6: Often done with the coil; $50–$150 depending on plug type and access.
Can I Still Drive With P0356?
You can usually drive for a short distance with P0356, but it’s not recommended to keep driving like that. A misfiring cylinder sends unburned fuel into the exhaust, which can overheat and damage the catalytic converter. You’ll also have reduced power, rough running, and possible stalling in traffic. If the check engine light is flashing, that’s a warning that the misfire is severe and you should avoid hard acceleration and get the vehicle checked as soon as possible.
What Happens If You Ignore P0356?
Ignoring P0356 can turn a relatively simple coil or wiring repair into a much more expensive catalytic converter or engine problem. Continuous misfires overheat the converter, can cause internal damage, and may even lead to raw fuel washing down cylinder walls, accelerating engine wear. Over time, you’ll also burn more fuel and risk being stranded with a no-start or severe drivability issue.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0355 – Ignition Coil “E” Primary/Secondary Circuit
Key Takeaways
- P0356 points to an electrical problem in the ignition coil circuit for cylinder 6, not just a generic misfire.
- Most cases are caused by a bad coil, damaged connector, or wiring issue rather than an ECU failure.
- Driving with P0356 can damage your catalytic converter and reduce performance and fuel economy.
- Basic tests like coil swapping, visual inspection, and simple meter checks can quickly narrow down the cause.
- Typical repair costs range from a couple hundred dollars for a coil to over a thousand if the ECU or harness is involved.
Vehicles Commonly Affected by P0356
P0356 shows up frequently on many V6 and V8 engines that use coil-on-plug ignition systems. You’ll commonly see it on Ford (F-150, Explorer, Mustang), GM/Chevrolet (Silverado, TrailBlazer, Equinox), Chrysler/Dodge/Jeep (Grand Cherokee, Charger, Durango), Toyota and Lexus V6 models (Camry, Highlander, Tacoma, RX), Nissan and Infiniti V6 engines (Altima, Maxima, Pathfinder, G35/G37), and various Hyundai/Kia V6 vehicles. High-mileage engines, vehicles with prior valve cover leaks, and those using cheap aftermarket coils tend to be more prone to this code.
FAQ
Can I clear P0356 myself and see if it comes back?
Yes, you can clear P0356 with a basic OBD-II scanner, but if the underlying problem isn’t fixed, the code and symptoms will return, often quickly. Clearing the code is fine after you’ve done a repair or swapped parts for testing, but don’t rely on clearing it as a “fix.”
Is P0356 always caused by a bad ignition coil?
No, P0356 is a circuit fault, not a guaranteed coil failure. While a bad coil is the most common cause, you can also have damaged wiring, a loose or corroded connector, or a failed ECU driver. That’s why simple tests like swapping coils and checking power/ground are important before buying parts.
How do I know which cylinder is number 6 on my engine?
Cylinder numbering depends on engine design and manufacturer. On many V6 engines, cylinder 6 is on the rear bank, which can be harder to access. Your owner’s manual, a repair manual, or an online diagram for your specific engine code will show the correct cylinder layout. Don’t guess, or you may test or replace the wrong coil.
Can bad spark plugs cause P0356?
Worn or incorrectly gapped spark plugs can overload the ignition coil and contribute to coil failure, which can in turn trigger P0356. While plugs themselves don’t usually set a coil circuit code directly, it’s smart to inspect and replace old plugs when you’re dealing with an ignition issue on that cylinder.
Can an ECU reflash or update fix P0356?
In rare cases, a manufacturer may release an ECU software update to improve misfire or ignition diagnostics, but a reflash alone usually won’t fix a true circuit fault. If the problem is a bad coil, wiring, or connector, you still need to repair or replace those components. An ECU reflash is only helpful if there’s a known software issue for your specific vehicle.