P0300-P0358 Ignition Coil Codes: What They Mean and What to Replace

OBD-II codes P0300–P0308 usually mean the engine is misfiring. Codes P0351–P0358 usually point more directly to an ignition coil primary or secondary circuit fault. If your scan tool shows both a cylinder misfire code and a coil circuit code, inspect the ignition coil, coil connector, wiring, spark plug, and PCM control circuit before replacing parts.

Important: Do not replace parts based only on the code. Use the code to identify the cylinder or circuit, then confirm the cause with inspection and testing.

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P0300–P0308 codes tell you where a misfire is happening. They do not always tell you why it is happening. The cause may be related to the ignition coil, spark plug, fuel delivery, air leaks, compression, or another engine system.

P0351–P0358 codes usually point more directly to an ignition coil primary or secondary circuit problem. That means the issue may be the coil itself, but it may also be the connector, wiring, power supply, ground, or PCM control circuit.

For example, P0351 is commonly defined as an ignition coil “A” primary or secondary circuit fault. It is not the same as a generic misfire code.

P0301 and P0351 may appear together, but they do not mean the same thing. P0301 tells you cylinder 1 is misfiring. P0351 points more specifically to ignition coil A or its circuit.

If you have P0301 only, test the ignition coil and spark plug instead of replacing the coil immediately. If you have P0351 plus P0301, inspect the ignition coil and coil circuit first.

Ignition coil codes can be caused by a failed coil, but the surrounding parts and circuits matter too. Check the full ignition path before deciding what to replace.

• Failed ignition coil
• Loose coil connector
• Damaged wiring
• Corroded terminal
• Oil or water in the spark plug well
• Bad spark plug
• PCM or ECM coil driver issue
• Poor ground or power supply
• Wrong coil part number
• Aftermarket coil not matched to the vehicle

1. Record All Codes

   Do not clear codes before recording them. Write down freeze-frame data if your scan tool shows it.

2. Identify the Cylinder

   A P0301 code points to cylinder 1. A P0302 code points to cylinder 2. For P0351–P0358, match the coil letter to the manufacturer’s cylinder layout.

3. Inspect Visible Issues

   Look for loose connectors, oil in the plug well, water intrusion, or a cracked coil boot.

4. Swap the Coil

   Move the suspected coil to a different cylinder and see whether the misfire follows the coil.

5. Replace the Confirmed Failed Part

   If the misfire follows the coil, replace the ignition coil. If the spark plug is worn, replace spark plugs at the same time.

You should avoid extended driving with an active misfire. Misfires can reduce power, increase fuel use, and may damage the catalytic converter if unburned fuel enters the exhaust. If the check engine light is flashing, stop driving and diagnose the issue immediately.