OBD-II trouble code
P0351: Ignition Coil 'A' Primary/Secondary Circuit
The engine computer detected a fault in the primary or secondary circuit of ignition coil 'A'. It usually means a bad coil, connector, or wiring on that cylinder, and it often comes with a misfire.
Quick facts
- System
- Powertrain
- Category
- Ignition
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $40 – $300
- DIY difficulty
- Intermediate DIY
What does P0351 mean?
On a coil-on-plug or coil-pack ignition system, each ignition coil steps battery voltage up to the tens of thousands of volts needed to jump the spark plug gap. The primary circuit is the low-voltage side the engine control module (ECM) switches on and off; the secondary circuit is the high-voltage side that feeds the spark plug. The ECM monitors the primary circuit and can infer secondary faults. P0351 sets when it detects an electrical problem — an open, a short, or an out-of-range condition — in the primary or secondary circuit of ignition coil 'A'.
The 'A' designation refers to a specific coil as mapped by the manufacturer. On many engines coil 'A' corresponds to cylinder 1, but the exact cylinder assignment varies, so always confirm against the vehicle's service information rather than assuming. Sister codes P0352 through P0358 cover the 'B' through 'H' coils.
Because a coil circuit fault usually means that cylinder isn't sparking properly, P0351 frequently appears alongside a misfire code such as P0300 (random misfire) or a cylinder-specific misfire like P0301. The engine may run rough, lose power, or trigger a flashing check engine light during an active misfire, which signals that raw fuel is reaching the catalytic converter and can damage it. The fault can lie in the coil itself, its connector, the wiring, or occasionally the ECM driver, so the circuit and connector should be checked before condemning the coil.
Common causes
- Failed ignition coil 'A' (most common)
- Corroded, loose, or damaged coil connector
- Open, shorted, or chafed primary or secondary circuit wiring
- Worn or fouled spark plug increasing load on the coil
- Poor ground or a supply-voltage problem to the coil
- Failed coil driver inside the ECM (less common)
Symptoms
- Check engine light on, sometimes flashing under load
- Engine misfire, rough idle, or shaking
- Loss of power and hesitation on acceleration
- Hard starting in some cases
- Reduced fuel economy
- Companion misfire codes such as P0300 or P0301
Diagnostic steps
- 1.Scan for all stored codes and note any accompanying misfire codes, which help confirm which cylinder is affected.
- 2.Confirm from service information which cylinder coil 'A' corresponds to on this specific engine.
- 3.Inspect the coil connector and wiring for corrosion, looseness, melted insulation, or chafing.
- 4.Swap coil 'A' with a coil from another cylinder. If the fault or misfire follows the coil, the coil is bad; if it stays put, suspect wiring or the spark plug.
- 5.Inspect the spark plug on that cylinder for wear, fouling, or an incorrect gap.
- 6.Check the coil's power feed and ground, and verify the primary control signal from the ECM before condemning the coil.
Repair cost
$40 – $300
A single ignition coil is commonly $40 to $200 in parts with 0.5 to 1.5 hours of labor, so a coil replacement is often $100 to $300. Many shops recommend replacing the spark plug on that cylinder at the same time. Wiring or connector repairs run $50 to $200. Replacing all coils as a set costs more but is common preventive practice on high-mileage engines.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with ignition coil replacement preselected. Adjust labor rate and vehicle category to fit your situation.
Related repairs
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.