P0351 is a diagnostic trouble code that points to an ignition coil problem on cylinder 1. When this code sets, your engine computer has detected a fault in the “A” coil primary or secondary circuit, which usually means a bad coil, wiring issue, or sometimes a failing ECU driver. You might notice rough running, misfires, or a flashing check engine light, especially under load. In this guide, you’ll learn what P0351 means in plain language, what typically causes it, what symptoms to watch for, and how you or your mechanic can fix it correctly.
What Does P0351 Mean?
P0351 stands for “Ignition Coil ‘A’ Primary/Secondary Circuit Malfunction.” On most vehicles, that “A” coil is the ignition coil for cylinder 1. The ECU constantly monitors the coil’s electrical signal. If the voltage or current pattern is outside the expected range, it flags P0351.
This can be caused by a failed coil, damaged wiring, poor connections, or in rare cases a faulty ECU coil driver. The result is usually a misfire on cylinder 1, especially under acceleration or at idle.
Quick Reference
- Code: P0351
- Meaning: Ignition Coil “A” (cylinder 1) circuit malfunction
- Severity: Moderate to high (can damage catalytic converter if ignored)
- Common Fix: Replace coil-on-plug unit and/or repair wiring
- Driveability: Often runs rough, may hesitate or stall
Real-World Example / Field Notes
In the shop, I see P0351 a lot on coil-on-plug engines. A typical case: a customer comes in with a flashing check engine light, rough idle, and complaint that the car “shakes” on the highway. Scan shows P0351 and a misfire on cylinder 1. Pull the coil and plug, and the coil boot is cracked with carbon tracking. Sometimes I’ll wiggle the coil connector with the engine running and the misfire comes and goes, confirming a loose terminal. A fresh coil, new plug, and cleaning or repairing the connector usually sends that car home running smooth again.
Symptoms of P0351
- Check engine light on, sometimes flashing under heavy load or acceleration
- Rough idle that feels like the engine is shaking or “loping”
- Engine misfire, especially noticeable when accelerating or climbing hills
- Loss of power and sluggish throttle response
- Poor fuel economy due to incomplete combustion in cylinder 1
- Hard starting or extended cranking, especially when the engine is cold or damp
- Exhaust odor of raw fuel or occasional popping from the exhaust
- Intermittent stalling at stops or when shifting into gear
Common Causes of P0351
Most Common Causes
- Failed ignition coil on cylinder 1: The internal windings or electronics in the coil break down, especially on high-mileage or heat-soaked engines.
- Cracked coil boot or insulation: Spark “leaks” to the engine block instead of the spark plug, often leaving visible carbon tracks.
- Worn or fouled spark plug: Excessive resistance or improper gap can overload the coil and trigger a circuit fault.
- Loose or corroded coil connector: Poor contact at the coil plug causes intermittent voltage and erratic coil operation.
- Damaged coil wiring: Chafed, pinched, or broken wires in the harness between the coil and ECU.
Less Common Causes
- ECU driver failure: The internal transistor that controls the coil fails, sending incorrect signals or no signal at all.
- Aftermarket performance parts: Poor-quality coils or plugs with incorrect heat range or gap can cause coil stress and circuit errors.
- Moisture intrusion: Water or oil in the spark plug well can short the coil to ground.
- Ground issues: Bad engine or chassis grounds can alter coil primary voltage and confuse the ECU.
- Previous wiring repairs: Poorly done splices, wrong gauge wire, or non-sealed connectors in the coil circuit.
Diagnosis: Step-by-Step Guide
To properly diagnose P0351, you’ll want at least a capable OBD2 scan tool, a basic digital multimeter, and ideally an oscilloscope for advanced checks. A spark tester and noid light can also help. If you’re comfortable with basic electrical tests and safe engine operation, you can do a lot of this yourself.
- Confirm the code and check for companions. Scan for P0351 and look for related misfire codes like P0301. Note freeze-frame data (RPM, load, temperature) to see when the fault occurred.
- Perform a visual inspection. With the engine off, remove the coil on cylinder 1. Look for cracks, burn marks, oil in the plug well, or green corrosion on the connector terminals.
- Swap coils between cylinders. Move the cylinder 1 coil to another cylinder and clear the codes. If the misfire and code move to that cylinder (for example, now P0352), the coil is bad.
- Inspect and test the spark plug. Check plug gap, wear, and deposits. Replace if worn, fouled, or oil-soaked. A cheap plug can cause an expensive coil to fail.
- Check coil power and ground. With key on, use a multimeter to verify battery voltage at the coil power wire. Confirm a good ground path if the coil uses a dedicated ground.
- Test the coil control signal. Using a test light or scope, check for a pulsed signal on the coil control wire while cranking or running. No pulse can indicate wiring or ECU issues.
- Inspect wiring harness. Gently tug and flex the harness from the coil back to the main loom. Look for rubbed-through insulation, sharp bends, or previous repairs. Repair any damaged sections with soldered, heat-shrunk splices.
- Check Mode $06 data (if available). Some scan tools let you view misfire counts by cylinder. This helps confirm that cylinder 1 is the main problem and not just a random misfire.
- ECU driver testing (advanced). If power, ground, and wiring are good, and a known-good coil still sets P0351, the ECU may have a failed coil driver. This usually requires professional testing or ECU replacement.
- Clear codes and road test. After repairs, clear the codes and perform a drive cycle under similar conditions to the freeze-frame data. Re-scan to confirm the code does not return.
Pro tip: If one coil has failed on a high-mileage engine and the rest are the same age, consider replacing the full set. It can save you from chasing repeated misfires and codes one coil at a time.
Possible Fixes & Repair Costs
Most P0351 repairs center around restoring proper spark and a clean electrical signal to the cylinder 1 coil. Costs vary with vehicle make, parts quality, and whether you do the work yourself or use a shop.
- Replace ignition coil on cylinder 1: $60–$180 for the part, plus $80–$150 labor at a typical shop.
- Replace spark plug(s): $8–$25 per plug, plus $60–$150 labor depending on access.
- Repair or replace coil connector: $20–$60 for a pigtail kit, plus $80–$150 labor.
- Repair wiring harness: $0–$50 in materials, $100–$250 labor depending on how deep the harness is buried.
- ECU replacement or repair (rare): $400–$1,200+ parts and programming, plus $150–$300 labor.
In many cases, you’re looking at roughly $150–$350 for a simple coil and plug replacement, while complex wiring or ECU issues can push the total much higher. Vehicle brand, engine layout, and local labor rates all affect the final bill.
Can I Still Drive With P0351?
You can sometimes drive with P0351, but it’s not recommended for long. If the engine is running very rough, shaking, or the check engine light is flashing, you should avoid driving and have it towed. A dead or weak coil means raw fuel can enter the exhaust, which overheats and damages the catalytic converter. Short trips to get home or to a repair shop are usually okay if the misfire is mild, but continuous driving can turn a simple coil job into a very expensive exhaust repair.
What Happens If You Ignore P0351?
Ignoring P0351 can lead to severe catalyst damage, higher fuel consumption, and long-term engine wear from unburned fuel washing down cylinder walls. Over time, you may also see additional misfire codes, fouled spark plugs, and hard-start issues. Fixing the problem early is far cheaper than replacing a catalytic converter or dealing with multiple failing coils later.
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
- P0351 means the ECU has detected an electrical problem in the ignition coil circuit for cylinder 1.
- Most cases are caused by a bad coil, worn spark plug, or wiring/connector issues.
- Symptoms include rough idle, misfires, loss of power, and a check engine light that may flash.
- Driving too long with P0351 can damage the catalytic converter and increase repair costs.
- Basic testing with a scan tool and multimeter can often pinpoint the fault before you start replacing parts.
Vehicles Commonly Affected by P0351
P0351 shows up on many modern vehicles that use coil-on-plug ignition. It’s especially common on:
- Ford F-150, Mustang, Explorer, Escape, and various V6/V8 engines known for coil failures.
- GM/Chevrolet models like Silverado, Tahoe, Malibu, and Equinox with individual coil packs.
- Toyota/Lexus 4-cylinder and V6 engines in Camry, Corolla, RAV4, Highlander, and ES/IS models.
- Chrysler/Dodge/Jeep vehicles with Pentastar V6 and HEMI V8 engines.
- Hyundai/Kia 2.0L, 2.4L, and V6 engines in sedans and crossovers.
- European brands like BMW, VW, and Audi, which are also known for coil-on-plug issues.
Any OBD2-equipped gasoline engine with individual coils can set P0351 when the cylinder 1 coil circuit acts up.
FAQ
Can P0351 be caused by a bad spark plug?
Yes. A worn, fouled, or incorrectly gapped spark plug can increase resistance and stress the coil, leading to P0351. It’s smart to inspect and often replace the spark plug on cylinder 1 when you’re dealing with this code.
Is P0351 the same as a misfire code?
Not exactly. P0351 points to an electrical problem in the ignition coil circuit for cylinder 1, while misfire codes like P0301 indicate that the cylinder isn’t firing properly. They often appear together, but P0351 focuses on the coil circuit itself.
How do I know if it’s the coil or the wiring causing P0351?
The easiest method is to swap the cylinder 1 coil with another cylinder and see if the code follows. If it does, the coil is bad. If it stays on cylinder 1, you likely have a wiring, connector, or ECU issue that needs further testing with a multimeter or scope.
Can I clear P0351 and keep driving if the car runs okay?
You can clear the code, but if the underlying issue is still there, it will come back. Even if the car seems to run “okay,” a weak or intermittent coil can get worse quickly. It’s best to diagnose and fix it rather than repeatedly clearing the code.
How urgent is it to fix P0351?
It’s fairly urgent. While the car might still move, a misfiring cylinder can overheat and damage the catalytic converter and cause long-term engine wear. Plan to address P0351 as soon as you can, especially if the check engine light is flashing or the engine runs very rough.