P0308 OBD-II Trouble Code: Cylinder 8 Misfire Detected

check engine light

P0308 Code Definition

Cylinder 8 Misfire Detected

What the P0308 code means

The P0308 trouble code means that the powertrain control module (PCM) has detected an issue with the ignition of the fuel being provided to cylinder 8. This must usually happen multiple times before a trouble code is stored and the Check Engine Light is illuminated.

What are the causes of the P0308 code?

Some potential causes of the P0308 trouble code would include:

  • Faulty ignition parts such as the spark plugs, ignition coils, spark plug boots and wires, or distributors

  • Faulty fuel system parts such as the fuel pressure regulator, fuel injectors, or the EGR valve

  • A large vacuum leak

  • A faulty powertrain control module

What are the symptoms of the P0308 code?

Some symptoms of the P0308 trouble code that the driver may experience would include:

  • Rough idle
  • Hesitation
  • Loss of power
  • Engine may die
  • Engine may not start
  • Decreased fuel economy

How does a mechanic diagnose the P0308 code?

The first thing a mechanic is likely to do when diagnosing a P0308 code is check the ignition system. If anything is visually wrong with the ignition system, such as something unplugged or broken, this issue would need to be resolved before any further diagnosis could take place.

If nothing is visually wrong with the ignition system, the mechanic would then test each spark plug and wire with an ignition tester to ensure that each plug is firing. If any issues is found during this test, they must be resolved before any further diagnosis can occur.

If no issues with the ignition system exist, the fuel system is the next stop for the mechanic. A fuel pressure test is likely to be performed to make sure that the fuel pressure regulator is functioning properly. Running data on the fuel injectors with an OBD-II scanner is another likely test the mechanic would perform on the fuel system. Any issues found with the fuel system are recommended to be repaired as soon as possible due to the fact that fuel is dangerous. A vacuum test may also be performed around the same time as the fuel pressure test to ensure the engine is producing sufficient vacuum.

If no issues are found with either of the previous two systems, the next step the mechanic would take is to use a high tech scan tool to test the powertrain control module for proper function. Any faulty parts found during this diagnosis would be replaced at the customer’s request.

Common mistakes when diagnosing the P0308 code

Easily the most common mistake when diagnosing a misfire code of any kind is replacing the spark plugs or doing a “tune up.” This procedure usually only has a 50/50 shot of repairing the problem without conducting proper diagnosis. Although spark plug failure is one of the top causes of a misfire, it is very important to assess every aspect of the problem before replacing any parts to avoid wasted time and money.

How serious is the P0308 code?

The P0308 code is a serious issue. This code being stored in a vehicle’s powertrain control module can prevent the engine from running well. It is important to many people’s daily lives that their vehicle performs properly and is able to get them from one place to another. This type of trouble code is one that could potentially leave a driver stranded on the side of the road. It is a good idea to find the root cause of the misfire and have it repaired as soon as possible.

What repairs can fix the P0308 code?

Repairs that can fix the P0308 code would include:

Additional comments regarding the P0308 code

A variety of things can cause a misfire. With this in mind, it is important to check for any and all possibilities before replacing parts. Most of the time a misdiagnosis will result from not taking the time to fully inspect and test every part of the system that has the issue.

Need help with a P0308 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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