Faulty ignition coil (Cylinder 1) (45% likelihood): The ignition coil for cylinder 1 has failed internally, either in the primary or secondary winding, and can no longer generate sufficient spark voltage. Damaged wiring or connector (25% likelihood): The wiring harness or electrical connector to the cylinder 1 ignition coil is damaged, corroded, or has a poor connection, interrupting the control signal. Worn or fouled spark plug (15% likelihood): A worn, fouled, or improperly gapped spark plug is causing excessive resistance in the secondary circuit, which can damage the coil and trigger this code. PCM driver circuit fault (10% likelihood): The PCM's internal ignition coil driver transistor for cylinder 1 has failed, preventing proper coil activation. Poor ground connection (5% likelihood): A corroded or loose ground connection at the coil or PCM is preventing proper circuit operation.

How much does it cost to fix P0351?

DIY repair typically costs $25–$80 for parts. Professional repair runs $100–$300 including parts and labor.

P0351

Powertrain

Moderate

Ignition Coil A Primary/Secondary Circuit Malfunction

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The P0351 code indicates a malfunction in the primary or secondary circuit of Ignition Coil A, which controls spark delivery to cylinder 1. Modern engines use individual coil-on-plug (COP) designs where each cylinder has its own ignition coil. When the PCM detects an abnormal signal in the coil's control circuit, it sets this code.

A flashing Check Engine light with this code means active misfires are occurring, which is more urgent than a steady light. Unburned fuel from a misfiring cylinder passes into the exhaust system and can overheat and damage the catalytic converter — an expensive component to replace. If the light is flashing, reduce your speed, avoid heavy acceleration, and get to a shop as soon as practical.

The quickest diagnostic approach is to swap the suspect coil with a coil from another cylinder. If the misfire and code follow the coil to the new cylinder, you've confirmed a bad coil. If the code stays on cylinder 1, the problem is in the wiring, connector, or PCM. Ignition coil replacement is one of the easiest DIY repairs — typically just unplug the connector, remove one bolt, and pull the coil out. Always replace the spark plug at the same time to protect the new coil.

Severity

Moderate — Address SoonThis Week

Symptoms

•Engine misfires or runs on fewer cylinders
•Check Engine light is on (may flash)
•Rough idle with noticeable vibration
•Loss of power during acceleration
•Strong fuel smell from exhaust
•Poor fuel economy

Likely Causes

Faulty ignition coil (Cylinder 1)45%

The ignition coil for cylinder 1 has failed internally, either in the primary or secondary winding, and can no longer generate sufficient spark voltage.

Damaged wiring or connector25%

The wiring harness or electrical connector to the cylinder 1 ignition coil is damaged, corroded, or has a poor connection, interrupting the control signal.

Worn or fouled spark plug15%

A worn, fouled, or improperly gapped spark plug is causing excessive resistance in the secondary circuit, which can damage the coil and trigger this code.

PCM driver circuit fault10%

The PCM's internal ignition coil driver transistor for cylinder 1 has failed, preventing proper coil activation.

Poor ground connection5%

A corroded or loose ground connection at the coil or PCM is preventing proper circuit operation.