Ignition Fault Codes: What They Mean, and How to Diagnose Them

A technician checks a car's ignition coils after learning it has an ignition trouble code indicating an ignition coil issue.

When diagnosing a problem with the ignition, the first thing to note is that the ignition fault codes in your powertrain control module (PCM) are not related to the ignition key. Ignition fault codes are related to the air and fuel mixture inside your engine not combusting properly.

Ignition Diagnostic Trouble Codes and What They Mean

A vehicle with ignition has spark in the cylinder applied at a specific time to create combustion. 

Diagnostic trouble codes related to the ignition are based on numbers assigned to each system of the car, which means P0300-P0399 are the ignition-related codes.

Cylinder Misfire Trouble Codes

Cylinder misfire trouble codes are easy for first-time do-it-yourselfers to read and make sense of. For instance, a P0300 code refers to a random cylinder misfire, meaning multiple cylinders are having an issue that could be related to the ignition. A misfire is the improper firing of the spark/fuel/air in a cylinder. 
P0301-P0312 are the individual cylinders having problems that would be read as 301—cylinder one, 302—cylinder two, etc.

Camshaft and Crankshaft Trouble Codes

Some other examples of ignition codes include the camshaft sensor, which reads the timing marks on a camshaft gear to ensure proper timing. 
In relation to the camshaft, the crankshaft also reads just the same via a reluctor wheel on the crankshaft by counting revolutions. These codes would typically appear as P0340 for camshaft sensor malfunction, or P0335 for a crankshaft reading incorrectly.

Ignition Coil Trouble Codes

Some other common ignition-related codes are P0350-359, which indicate a circuit issue with the ignition coils, meaning there could be a break in a wire or a faulty ignition coil.

How to Diagnose Ignition Trouble Codes

Use a Reliable OBD-II Scan Tool to Diagnose and Troubleshoot

Higher-End Scan Tool Benefits for Diagnosing Ignition Codes

You rarely need an expensive OBD2 scan tool to diagnose an ignition issue—an inexpensive one will do just fine. 

While most scan tools will read ignition fault codes P0300 to P0399, some will also have a misfire counter, which shows you the misfiring cylinders in real-time. This feature can be very helpful when diagnosing an engine with ignition problems because it’ll narrow down the problem part fast. 

You can still narrow down the issue to a specific cylinder with a simpler scan tool. You may just need to take the car for a few quick additional test drives to narrow the problem down to a precise part.

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How to Diagnose a Failing Ignition Coil

This example is the easiest way to diagnose a failed ignition coil. If you have a code P0302 showing cylinder 2 is a misfire or code P0352, you can swap the ignition coil with the cylinder next to it. Next, clear the codes with a scan tool. Then start the engine and monitor that cylinder to see if the misfire code has moved to the new cylinder, or if it’s still misfiring at cylinder 2.

How to Diagnose a Misfire

Look Up the Firing Order to Find How the Cylinders Are Laid Out

To understand how the cylinders could be affected by the ignition failure, you must first understand how the cylinders are laid out in the engine. 
Typically, cylinder 1 is the forward most cylinder to the harmonic balancer or timing components.

Inline Engine 

In an inline engine, the cylinders will read, “1-2-3-4-5-6-7-8-,” etc.


In a V-series engine, they can be odds on one side and evens on the other, like in most GM vehicles, or in order from the right-back and then the front-back on the driver side. 

The best way to find out your car’s cylinder layout is to look up “Firing Order” in your owner’s manual.

Visually Inspect Ignition-Related Parts 

If you’re diagnosing a misfire, you’ll mostly be looking at external components, such as spark plugsinjectors, spark plug leads/wiresignition coilsdistributors, or caps when applicable, bad fuel or electrical parts, such as plugs or wiring, or an ignition module when applicable.

Is It Safe to Drive with an Engine Misfire?

It’s not safe to drive with an engine misfire. Whenever the engine isn’t firing properly, you run the risk of internal damage. If the engine is misfiring, you want to address it immediately. An unaddressed misfire can damage the catalytic converter or internal engine components.

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How-to Videos: Learn How to Do More than Diagnose Ignition Fault Codes

Learn how to do more than diagnose ignition fault codes. Our how-to videos can help you remove and install parts on specific models with step-by-step instructions, pick up general automotive tips, and more.

Fix ignition fault codes in your vehicle yourself with quality auto parts and tips at 1aauto.com
Ignition Fault Codes: What They Mean & How to Diagnose - 1A Auto
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Ignition Fault Codes: What They Mean & How to Diagnose - 1A Auto
We're breaking down common ignition fault codes, what they mean, and how to diagnose common ignition issues with the help of an OBD2 scan tool.
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