OBD-II Trouble Codes

P0351 Code: Ignition Coil A Primary / Secondary Circuit

Reading Time: 3 minutes

Your vehicle’s ignition coils provide the high voltage needed to ignite the spark plugs. Most modern vehicles have an individual coil-on-plug ignition coil for each of the engine’s cylinders.

Ignition coils can fail for a variety of reasons. In some cases, the insulation of the coil gets damaged, causing a short. In other cases, the problem stems from bad spark plugs and wiring issues.

The P0351 code may appear when your car’s primary computer, which is often referred to as the powertrain control module (PCM), perceives a problem with the cylinder #1 ignition coil or its circuit.

a car's ignition coil
Code P0351 indicates that there’s a potential problem with the cylinder #1 ignition coil or its circuit.

What Does the P0351 Code Mean?

Diagnostic Trouble Code (DTC) P0351 stands for “Ignition Coil ‘A’ Primary/Secondary Circuit.” It indicates that there’s a potential problem with the cylinder #1 ignition coil or its circuit.

An ignition coil contains two sets of windings that wind around an iron core. The ratio of primary and secondary windings inside an ignition coil determines the output voltage of the coil. When current flows to the ignition coil, it flows through the primary windings in such a way that it generates a strong magnetic field.

The magnetic field that the ignition coil produces collapses once the ground connection gets established and the primary windings turn off. The energy from the magnetic field then goes to the secondary windings of the ignition coil. There, the voltage multiplies and the ignition coil produces enough voltage to fire the spark plug.

Most modern engines equip a coil-on-plug (COP) ignition system. This means that each cylinder has an individual coil under the control of the PCM. If one of the ignition coils doesn’t function properly, the vehicle could stumble and misfire.

If the P0351 code registers in your vehicle, you need to address it immediately. Repairs may be of moderate difficulty, so it’s best to consult your diagnostic and repair guides or your mechanic to fix the problem.

Note: The definition of code P0351 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

mechanic fixing a faulty engine
Engine misfires that get worse upon acceleration are a common symptom of the P0351 code.

What are the Possible Causes of the P0351 Code?

OBD-II codes have several possible causes, and the P0351 code is no different. Below are some of the most likely causes of the P0351 code:

What are the Common Symptoms of the P0351 Code?

A combination of the symptoms listed down below may indicate that you’re dealing with the fault code P0351. As soon as you encounter these symptoms, use a scanner to verify the issue.

How to Diagnose the P0351 Code

Given that the engine code P0351 has multiple likely causes, doing a proper diagnosis of the problem can prove quite a challenge. Luckily, there are a lot of online resources for the average DIYer to help with this process. Here is a link to a video resource that shows what the troubleshooting process might involve for the P0351 code:

How to Fix the P0351 Code

After diagnosis, the next step to fixing the P0351 code is research. Search for confirmed fixes that are specific not only to what triggered the code in your vehicle but also to your car’s year, make, and model. Consult online auto repair resources and guides for factory information.

If you’re not certain that your automotive knowledge and DIY repair skills are up to the task, it may be best to let your mechanic resolve the issue.

Other Notes About P0351

If your vehicle’s computer detects a problem in the ignition coil circuit, it may send the ignition coil circuit codes P0351-P0358. The last digit of these codes refers to the cylinder where the issue is located. Repair and diagnosis procedures might differ according to the cylinder. Ignition coil problems often trigger the misfire codes P0300-P0308.

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