An engine needs three elements to run: compression, spark, and a precise air/fuel mixture. When an engine cylinder misfires, the root cause originates from an issue with one of these three factors.
Driving your vehicle despite one or more of the cylinders misfiring may damage the engine. The P0308 code indicates that the powertrain control module (PCM) has detected a misfire on cylinder #8.
What are the repercussions of this trouble code, and what can you do to remedy the problem? Read this short guide to find out more.
What Does the P0308 Code Mean?
Diagnostic trouble code (DTC) P0308 stands for “Cylinder 8 Misfire Detected.” It indicates that the PCM perceives a misfire on cylinder #8.
Cylinder number 8 would refer, not to the eighth cylinder in the firing order, but the cylinder numbered “8” in the arrangement of cylinders on the engine.
A misfire is caused either by incomplete combustion (or the absence of combustion) in one cylinder. Combustion is a small explosion that takes place when a pressurized air-fuel mixture is ignited inside the combustion chamber above each piston, and these explosions are timed very precisely for optimum power and efficiency.
Cylinder number 8 would refer, not to the eighth cylinder in the firing order, but the cylinder numbered “8” in the arrangement of cylinders on the engine.– Richard McCuistian, ASE Certified Master Automobile Technician
The combustion event superheats the inert nitrogen (which is 78% of the air charge) and the superheated nitrogen expands to drive the piston downward, which, applies torque by way of the connecting rods to the crankshaft, creating the rotational force delivered to the transmission or transaxle, which applies torque to the drive wheels. When a cylinder misfires, the crankshaft slows just a bit because the cylinder’s combustion event either didn’t take place or was weak.
The P0308 is associated with other engine misfire codes, specifically codes P0300 to P0312.
If you need more information to locate cylinder #8, read our explanation about cylinder location and firing order. Make sure you completely understand how cylinder misfires are identified by the PCM before attempting any DIY diagnosis or fix for code P0308.
What are the Possible Causes of the P0308 Code?
As mentioned above, misfires can trace their origin to a variety of factors. In the case of the P0308 code, these are the most common causes:
- Bad spark plug
- Faulty spark plug wire
- Failed ignition coil
- Faulty fuel injector
- Engine mechanical problem
- Defective computer (rare)
Note: If additional misfire codes are stored, the list of potential causes may differ.
What are the Common Symptoms of the P0308 Code?
Listed below are just some common symptoms of the P0308 code. Note that you may encounter a combination of the signs below. Once you notice any of these issues, it’s a good practice to immediately check if the P0308 code or any other misfire code has been set. This is to avoid further damage to your engine and other parts of your vehicle.
- Check engine light is on or flashing
- Engine is hard to start
- Engine runs rough
- Engine is shaking
- Lack of engine power
- Fuel smell from exhaust
- Hesitation/jerking when accelerating
- Other symptoms may also be present
How to Diagnose the P0308 Code
Diagnosing OBD-II codes may seem intimidating because you need to pinpoint their exact cause before attempting any repairs. And with the engine code P0308, there are quite a few causes.
If you’re a seasoned DIYer, there are a lot of repair guides and tutorials available online and in print to help you diagnose the code properly. Below are two online video resources that you can use to understand P0308 code and other misfire-related problems better:
How to Fix the P0308 Code
Figuring out a P0308 code fix is challenging, but it is possible. The key to determining the chief cause and an appropriate repair plan is to arm yourself with knowledge about how your vehicle works. Then, read up on what the error code is about.
Note that there is no single fix for each OBD-II code and that repair steps will vary depending on the vehicle’s make and model.
Good thing there are repair manuals and guides with helpful illustrations available in the market, such as ALLDATA. Getting a subscription for repair guides is great, especially if you’re a dedicated DIYer. However, if you’re unsure about making a diagnosis and repairing your vehicle on your own, you can always have your mechanic do the job for you.
Other Notes About P0308
The P0308 is an OBD-II code with a high repair importance level. This means that it must be addressed right away. Ignoring this code might lead to one or more of the following scenarios:
- Catalytic converter damage
- Internal engine failure
- Dangerous conditions while operating the vehicle
If you encounter this code, you must stop driving the vehicle and bring it to a shop for repairs immediately. The engine code P0308 has a high repair difficulty level and it might be best to let your mechanic deal with the issue, especially if you’re not confident in your skills as a DIYer.
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