P0355 is an ignition coil circuit trouble code that can cause rough running, misfires, and a flashing Check Engine Light. It points you toward a specific coil circuit, not the entire ignition system, which helps narrow down the problem. In most vehicles, P0355 refers to Ignition Coil “E” or Coil #5, depending on the manufacturer. You might be dealing with a bad coil, broken wiring, or an ECU driver fault. With some basic tools and a methodical approach, you can track it down and decide if it’s a DIY job or shop visit.
What Does P0355 Mean?
P0355 is defined as “Ignition Coil E Primary/Secondary Circuit Malfunction.” On most multi-coil systems (coil-on-plug or coil-near-plug), each cylinder has its own ignition coil controlled by the engine control unit (ECU). This code tells you the ECU has detected an electrical problem in the circuit for the fifth coil (often cylinder #5, but always verify by service info for your engine).
The ECU monitors coil control and feedback signals. If it sees voltage that’s too high, too low, intermittent, or completely missing on that specific coil circuit, it sets P0355 and may also log misfire codes for the same cylinder.
Quick Reference
- Code: P0355 – Ignition Coil E Primary/Secondary Circuit
- Severity: Moderate to severe – can cause drivability issues
- Common causes: Failed ignition coil, wiring damage, loose connector, ECU driver fault
- Typical symptoms: Misfire, rough idle, loss of power, poor fuel economy
- Risk: Possible catalytic converter damage if driven misfiring for long
Real-World Example / Field Notes
In the shop, I see P0355 a lot on higher-mileage coil-on-plug engines. A typical case: a customer comes in with a flashing Check Engine Light, rough running, and a strong fuel smell. Scan tool shows P0355 and a misfire code on cylinder 5. A quick coil swap test (moving coil 5 to another cylinder) makes the misfire follow the coil. Replacing that single coil and clearing codes fixes it. Other times, especially on vehicles that had rodent damage or DIY plug changes, I find broken coil wires or half-seated connectors causing an intermittent P0355 that only shows up under load or when the engine moves in its mounts.
Symptoms of P0355
- Check Engine Light – solid or flashing, often with stored misfire codes
- Rough idle – engine shakes or feels uneven, especially at stoplights
- Loss of power – sluggish acceleration, poor performance under load
- Engine misfire – noticeable stumble, especially when accelerating or climbing hills
- Poor fuel economy – you may notice more frequent fuel stops
- Fuel smell from exhaust – unburned fuel due to misfiring cylinder
- Hard starting – extended crank time or rough start, especially when cold
- Occasional stalling – in severe or intermittent circuit failure cases
Common Causes of P0355
Most Common Causes
- Failed ignition coil E / coil #5 – internal short or open in the coil windings is the number one cause.
- Loose or corroded coil connector – poor contact at the coil plug can interrupt the primary circuit.
- Damaged coil wiring – broken, chafed, or oil-soaked wires between the coil and ECU.
- Faulty spark plug – a severely worn or shorted plug can stress the coil and trigger circuit faults.
- Aftermarket or low-quality coils – cheap replacements often fail prematurely or have incorrect resistance.
Less Common Causes
- ECU driver failure – the internal transistor that controls that coil circuit can burn out.
- Short to power or ground – wiring harness pinched, melted, or rubbed through on brackets or the engine.
- Moisture intrusion – water or oil in the spark plug well causing arcing and abnormal coil current.
- Previous engine work errors – coil connectors swapped, wires routed incorrectly, or pins bent during repairs.
- Poor engine ground – weak ground paths can affect coil operation and confuse ECU monitoring.
Diagnosis: Step-by-Step Guide
Basic tools you’ll want: an OBD-II scan tool (preferably one that shows live data and Mode $06), a digital multimeter, a spark tester or known-good coil, and basic hand tools. A wiring diagram and access to service information for your specific vehicle are also very helpful.
- Confirm the code and note freeze-frame data. Scan for P0355 and any related misfire codes (like P0305). Check engine RPM, load, and temperature at the time the code set to know when the fault occurs.
- Perform a visual inspection. Locate coil “E” or coil #5 using a service manual. Inspect the coil, connector, and nearby harness for cracks, burn marks, oil contamination, or loose plugs.
- Check for obvious misfire. With the engine idling, listen and feel for misfire. If safe, disconnect the suspected coil’s connector briefly; if idle doesn’t change, that cylinder is likely already misfiring.
- Swap coils to isolate the fault. Move the suspected coil to another cylinder and move that cylinder’s coil to the original position. Clear codes and test drive. If the misfire and code move to the new cylinder, the coil is bad.
- Test coil power and ground. With the key on, use a multimeter to verify battery voltage on the coil power feed and a good ground on the ground circuit. Repair any open or high-resistance connections.
- Check the coil control signal. Using a test light or scope (best), confirm the ECU is pulsing the control wire while cranking or running. No pulse may indicate a broken wire or bad ECU driver.
- Inspect wiring continuity. If control signal is missing, check continuity from the coil connector back to the ECU pin. Repair any open, short-to-ground, or short-to-power conditions found.
- Review Mode $06 data. On some vehicles, Mode $06 will show misfire counts by cylinder. High counts on one cylinder support a coil or plug issue rather than a random wiring problem.
- Check the spark plug. Remove and inspect the plug for wear, cracks, oil fouling, or incorrect gap. Replace if questionable, especially if it’s old or mismatched.
- Evaluate ECU only after other causes are ruled out. If power, ground, wiring, coil, and plug all check out, and there’s still no control signal, you may be looking at an ECU fault. At this point, professional testing or ECU replacement may be needed.
Pro tip: When replacing a failed coil for P0355, inspect all coils and plugs on that bank. If one has failed due to age and mileage, the others may not be far behind, and doing them together can save you future labor and downtime.
Possible Fixes & Repair Costs
Most P0355 repairs are straightforward once you pinpoint the cause. Common fixes include replacing the affected ignition coil, repairing or replacing damaged wiring, cleaning and securing the coil connector, and installing new spark plugs if they’re worn or fouled. In rare cases, the ECU must be repaired or replaced and programmed.
Typical repair costs vary by vehicle and shop rate. A single ignition coil replacement usually runs about $100–$300 parts and labor. Coil plus spark plug replacement on that cylinder can land in the $150–$400 range. Wiring repairs may be $100–$250 depending on access. An ECU replacement is the big-ticket item, often $600–$1,200+ including programming. Costs depend on brand, parts quality (OEM vs aftermarket), and how difficult your engine layout is to work on.
Can I Still Drive With P0355?
You can often still drive with P0355, but it’s not a good idea to ignore it. If the engine is misfiring badly, especially with a flashing Check Engine Light, you risk damaging the catalytic converter from raw fuel entering the exhaust. Short trips to get home or to a shop are usually fine if the car is still drivable, but avoid heavy acceleration, towing, or highway passing. If the engine is shaking violently, stalling, or the light is flashing constantly, have it towed to prevent further damage.
What Happens If You Ignore P0355?
Ignoring P0355 can turn a relatively small ignition repair into a much larger bill. Continuous misfires overheat and melt the catalytic converter, foul oxygen sensors, and can wash down cylinder walls with fuel, reducing engine life. You’ll also burn more fuel and may fail emissions testing. Addressing the code promptly almost always costs less than waiting until additional components fail.
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
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
Key Takeaways
- P0355 points to an electrical problem in the ignition coil E (often cylinder #5) primary/secondary circuit.
- Most cases are caused by a bad coil, poor connector contact, or damaged wiring, not the ECU.
- Symptoms include misfire, rough idle, loss of power, and a Check Engine Light that may flash under load.
- Driving for long with a P0355 misfire can damage your catalytic converter and increase repair costs.
- Proper diagnosis includes visual inspection, coil swap tests, voltage checks, and wiring continuity tests.
- Repairs typically range from about $100–$400 for coil and plug issues, more if wiring or ECU is involved.
Vehicles Commonly Affected by P0355
P0355 shows up across many modern vehicles that use coil-on-plug ignition systems. It’s commonly seen on Ford and Lincoln V6 and V8 engines, especially 4.6L, 5.4L, and 3.5L EcoBoost platforms. Toyota and Lexus V6 engines, such as the 3.0L and 3.3L, also see this code with aging coils. Nissan and Infiniti VQ-series V6s, Chrysler/Dodge/Jeep 3.6L and 5.7L engines, and various GM V6/V8 trucks and SUVs are frequent visitors to the shop with coil circuit codes, including P0355. High mileage, heat, and oil leaks into plug wells all contribute to coil failures on these platforms.
FAQ
Can I clear P0355 and keep driving if the car feels normal?
You can clear the code, but if the underlying issue isn’t fixed, P0355 will likely return. Even if the engine feels normal now, an intermittent coil or wiring problem can get worse and suddenly cause a hard misfire. It’s better to diagnose and repair the cause rather than rely on clearing the code.
Is P0355 always the ignition coil itself?
No. The coil is the most common failure, but P0355 is a circuit code. It can be caused by bad wiring, a loose connector, poor power or ground, or even an ECU driver fault. That’s why a quick coil swap test and some basic electrical checks are important before buying parts.
How do I know which cylinder is “coil E” on my engine?
“Coil E” usually corresponds to cylinder #5, but not on every engine. The exact mapping depends on your manufacturer’s labeling. Check a service manual or reliable repair database for your specific year, make, and model. Many scan tools and factory diagrams will show the coil letter-to-cylinder relationship.
Can a bad spark plug cause P0355?
Yes, indirectly. A severely worn, cracked, or shorted spark plug can overload the ignition coil, causing it to draw abnormal current. Over time, that can damage the coil and trigger a circuit fault like P0355. That’s why it’s smart to inspect and often replace the spark plug when you fix a coil-related code.
How urgent is it to fix P0355?
You should address P0355 as soon as you can. If the engine is misfiring, continued driving can overheat and damage the catalytic converter and other components. If the car runs relatively smooth and the misfire is light or intermittent, you may have some time, but it’s still best to diagnose and repair it before it gets worse.