P0359 is an ignition system trouble code that points specifically to a problem with ignition coil “I” (coil number 9 on most systems). When this code sets, your engine computer has detected an electrical fault in that coil’s primary or secondary circuit. You might notice rough running, misfires, or a flashing check engine light, especially under load. While it can be as simple as a bad coil or spark plug, wiring and ECU issues are also possible. Understanding what P0359 means helps you avoid unnecessary parts swapping and protect your engine and catalytic converter.
What Does P0359 Mean?
P0359 stands for “Ignition Coil I Primary/Secondary Circuit Malfunction.” On coil-on-plug (COP) systems, each cylinder has its own ignition coil. The ECU controls each coil and monitors the electrical signal. When it sees voltage or current outside the expected range for coil I, it sets P0359 and may also log a misfire code for that cylinder.
In simple terms, the computer is telling you that the electrical path that fires one specific coil is faulty. This can be caused by the coil itself, the wiring and connectors, or less commonly the ECU driver circuit.
Quick Reference
- Code: P0359
- Meaning: Ignition Coil I (9) Primary/Secondary Circuit Malfunction
- Severity: Moderate to high (misfire risk, possible catalyst damage)
- Common Fix: Replace faulty ignition coil or repair wiring
- Driveability: Often runs rough; avoid hard driving until repaired
Real-World Example / Field Notes
In the shop, I see P0359 most often on higher-mileage V8 and V10 engines that use coil-on-plug setups. A typical case: truck comes in with a flashing check engine light under load and a noticeable shudder on the highway. Scan shows P0359 plus a misfire code for cylinder 9. A quick coil swap test (moving coil 9 to another cylinder) makes the misfire follow the coil. New coil, fresh plug, clear the codes, and the truck is back to smooth power. On other jobs, corroded connectors or rodent-chewed wiring have been the real culprits, so you don’t want to assume it’s always the coil.
Symptoms of P0359
- Check engine light on solid or flashing, sometimes accompanied by additional misfire codes
- Engine misfire, especially under acceleration or climbing hills
- Rough idle or shaking at stoplights, sometimes with engine vibration felt in the seat or steering wheel
- Loss of power and sluggish acceleration, particularly at higher speeds
- Poor fuel economy due to incomplete combustion and unburned fuel
- Exhaust odor of raw fuel or “sulfur/rotten egg” smell from stressed catalytic converters
- Hard starting or longer crank time in some cases
- Intermittent stumble when hitting bumps if wiring or connectors are loose
Common Causes of P0359
Most Common Causes
- Failed ignition coil on cylinder 9 (internal short or open in the coil windings)
- Worn or fouled spark plug causing excessive load on the coil
- Damaged ignition coil connector (broken lock tab, loose pins, corrosion)
- Broken, chafed, or shorted wiring between the coil and ECU
- Oil or moisture intrusion in the spark plug well causing arcing
Less Common Causes
- ECU (PCM) driver failure for the coil I circuit
- Aftermarket remote start or alarm wiring spliced into ignition circuits
- Previous engine work leaving a pinched harness or partially plugged connector
- Incorrect or low-quality replacement ignition coil or plug
- Internal engine issues (low compression, valve problems) that show up alongside ignition faults
Diagnosis: Step-by-Step Guide
To diagnose P0359 properly, you’ll want at least a good OBD2 scan tool, a digital multimeter (DMM), and basic hand tools. An oscilloscope and access to wiring diagrams or service information make the job easier, but you can still do solid diagnosis with basic equipment and patience.
- Confirm the code and check for companions. Scan the vehicle and note any related misfire codes (like P0309) or other ignition codes. Freeze-frame data will show engine load and RPM when the fault occurred, which helps identify if it’s load-related or constant.
- Perform a visual inspection. Locate coil I (usually cylinder 9; check your firing order). Inspect the coil, connector, and harness for cracks, oil contamination, broken locking tabs, or obvious damage. Look for signs of arcing or burn marks around the coil boot.
- Check for moisture and oil in the plug well. Remove the coil and inspect the spark plug tube. Oil from a leaking valve cover gasket or water intrusion can cause misfires and circuit faults. Clean and dry the area before reassembly.
- Swap test the ignition coil. Move the suspect coil from cylinder 9 to another cylinder (for example, cylinder 1) and clear the codes. Drive or run the engine while monitoring for new codes. If the misfire and P0359 move to the new cylinder, the coil itself is bad.
- Inspect and test the spark plug. Remove the spark plug from cylinder 9. Check for worn electrodes, heavy deposits, cracks, or incorrect gap. Replace if questionable. A failing plug can overload the coil and trigger P0359.
- Check coil power and ground. With the key on (engine off), back-probe the coil connector using a wiring diagram. Verify you have proper battery voltage at the power feed and a solid ground. Repair any open or corroded power/ground circuits.
- Test the coil control signal. With the engine cranking or running, use a test light or scope on the ECU control wire to the coil. You should see a pulsed signal. If other coils have a good signal and coil I does not, suspect wiring or ECU driver issues.
- Check wiring continuity. With the ignition off, unplug the ECU and the coil connector. Use your multimeter to check resistance from the coil control pin to the ECU pin. High resistance, an open circuit, or continuity to ground where it shouldn’t exist indicates a wiring fault.
- Review Mode $06 data (if available). Some scan tools let you look at cylinder-specific misfire counts in Mode $06. This can confirm that cylinder 9 is the main offender and help verify repairs.
- Evaluate ECU only after all else checks out. If the coil, plug, power, ground, and wiring are all verified good and the signal from the ECU is missing or erratic only on coil I, you may be dealing with a failed ECU driver. This is rare and should be confirmed carefully.
Pro tip: When replacing a single failed coil on a high-mileage engine, consider replacing the spark plug on that cylinder at the same time. If several coils are original and one has failed, you may prevent future breakdowns by replacing coils in pairs or as a bank, depending on your budget.
Possible Fixes & Repair Costs
Most P0359 repairs involve replacing the affected ignition coil, repairing wiring, or addressing spark plug and oil intrusion issues. Typical shop repair costs range from about $150–$350 for a single coil and plug replacement, up to $400–$800 if wiring repairs or multiple coils are needed. ECU replacement and programming, if required, can push costs to $700–$1,500 or more. Labor rates, parts quality (OEM vs aftermarket), engine layout (easy vs buried coils), and diagnostic time all influence the final bill.
- Replace ignition coil on cylinder 9
- Replace spark plug(s) and set correct gap
- Repair or replace damaged coil connector and terminals
- Repair chafed, broken, or corroded wiring between ECU and coil
- Fix oil leaks from valve cover gaskets and clean plug wells
- Reprogram or replace ECU if the driver circuit is confirmed faulty
Can I Still Drive With P0359?
You can usually drive short distances with P0359, but it’s not recommended to ignore it or continue driving hard. A misfiring cylinder sends raw fuel into the exhaust, which can quickly overheat and damage the catalytic converter. You may also experience reduced power and poor throttle response, which can be unsafe when merging or passing. If the check engine light is flashing or the engine is running very rough, treat it as urgent: reduce load, avoid highway speeds, and get the vehicle inspected as soon as possible.
What Happens If You Ignore P0359?
Ignoring P0359 can turn a relatively simple ignition repair into a much more expensive job. Long-term misfires can melt or clog catalytic converters, foul oxygen sensors, and cause additional coil failures. The constant vibration and unburned fuel can also accelerate wear on engine mounts and internal components. Addressing the code early usually saves you money and keeps the engine running smoothly.
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
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
- P0355 – Ignition Coil “E” Primary/Secondary Circuit
Key Takeaways
- P0359 points to an electrical problem in the ignition coil I (usually cylinder 9) primary/secondary circuit.
- Most cases are caused by a bad coil, worn spark plug, or wiring/connector issues.
- Symptoms include misfires, rough idle, loss of power, and a check engine light that may flash.
- Driving for long with P0359 can damage the catalytic converter and other components.
- Proper diagnosis—coil swap tests, wiring checks, and scan data—prevents unnecessary parts replacement.
- Typical repair costs range from a couple hundred dollars for a coil and plug to much more if wiring or the ECU is involved.
Vehicles Commonly Affected by P0359
P0359 shows up most often on vehicles with V8, V10, or high-cylinder-count engines that use coil-on-plug ignition. In the real world, you’ll commonly see it on full-size pickup trucks and SUVs from Ford, GM (Chevrolet, GMC, Cadillac), and Ram, as well as some performance cars and larger SUVs from manufacturers like Toyota, Lexus, Nissan, Infiniti, BMW, and Mercedes-Benz. Any modern engine with individual coils can set this code, especially as mileage climbs and heat cycles take a toll on coils and wiring.
FAQ
Can I clear P0359 and keep driving if the car feels okay?
You can clear the code, but if the underlying problem is still there, P0359 will almost always return. Even if the engine feels okay now, intermittent coil or wiring issues tend to get worse. It’s better to diagnose and fix the cause rather than repeatedly clearing the light.
Is P0359 always caused by a bad ignition coil?
No. A bad coil is very common, but not guaranteed. Wiring faults, loose connectors, oil in the plug well, and even ECU driver problems can all trigger P0359. A quick coil swap test and basic electrical checks help you avoid replacing a good coil.
How do I know which cylinder is coil I / cylinder 9 on my engine?
The cylinder numbering and coil labeling depend on your engine design. Typically, cylinder 1 is at the front of the engine, and numbering follows a specific pattern. Your owner’s manual or a service manual will show the firing order and cylinder layout. Many scan tools and service databases also map P0359 to the correct cylinder for your specific vehicle.
Can a bad spark plug cause P0359?
Yes. A severely worn, fouled, or cracked spark plug can increase the voltage demand on the coil and lead to ignition coil circuit faults. When dealing with P0359, it’s smart to inspect and, if needed, replace the spark plug on that cylinder along with any suspect coil.
How urgent is it to fix P0359?
You should address P0359 as soon as possible. While the car may still run, driving with an active misfire risks damaging the catalytic converter and other components. If the check engine light is flashing or the engine runs very rough, minimize driving and get it inspected right away.