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P0309 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Cylinder 9 Misfire Detected


When the P0309 trouble code appears, it means that the powertrain control module has found a misfire from cylinder number 9.  When your car shows you the P0309 trouble code, you need to check for possible causes and take corrective action to fix your car as soon as possible.


There are a number of different causes that could bring up the P0309 trouble code including:

  • Loose or damaged plug wires
  • Damaged coil pack
  • Bad spark plugs 
  • Fuel injector failure
  • Fuel pressure regulator issues 
  • Leaks in the intake manifold gasket or vacuum hoses.


P0309 trouble code starts with you seeing the service engine light on your car’s dashboard and that will give an indication of a problem with one of your cylinders. The P0308 is often accompanied by other codes, so it’s best to have them checked out if they show up as well. Most car mechanics charge a fee for running the P-code on your vehicle, however, there are some free online resources where you can get the diagnosis done when you have P0309 trouble codes. Other possible causes could be lack of fuel or an ignition control module that gets its signals mixed up causing several cylinders not to fire when they should.


The mechanic can start with checking for loose or damaged plug wires, bad spark plugs. After that, replace the coil pack with a new one of OEM quality and test drive your car to see if the same symptom occurs again on your original cylinder number 9 or other cylinders. Always remember that depending on what type of diagnostic testing is done will also determine how long the diagnosis process takes.  

Common mistakes

Mechanics may believe that the problem lies in the ignition system rather than other areas. P0309 problems may also be caused by dirty or defective spark plugs, bad coil packs, shorted plug wires, and loose or fouled spark plugs.   

How serious is this?

P0309 trouble code will not disable your vehicle, so you shouldn’t experience any drivability problems with your car. What may leave you stranded though when the P0309 code shows up on your dashboard is that it’s usually accompanied by other obd codes.

What repairs can fix the code?

There are three steps that you can use as guidelines to troubleshooting this P0309 code:

  1. Check for obvious problems such as loose or damaged plug wires, bad spark plugs, etc.
  2. If a problem still exists after your check, replace the coil pack with a new one of OEM quality. 
  3. Lastly, test drive the car and see if the same symptom occurs again on your original cylinder number 9 or other cylinders.

Related codes

P0309 Code is hard to interpret for many novice car technicians due to lack of experience and training. This P0309 code usually comes with 

How much does it cost to fix the P0309 code? 

A basic diagnostic fee can run between $100.00 and $200.00 depending on where you go and who you ask. After that price quote, a more accurate number is derived based on how long it takes to find out what’s wrong with your car when the checkup begins. On average though, at present rates, most shops charge about an hour for labor minus diagnostic time which is around $100-150.


Even if you have a mechanic to help fix your car, it’s good for people who are interested in cars to know what some of the codes mean. In this post, we covered P0309 and how to fix it. You may want to bookmark this page so that next time you need information about an OBD code, you can find it quickly! If you found our blog posts helpful or interesting, please share them with others on social media by clicking one of the buttons below. Thanks for reading!

P0309 – What Does It Mean and How To Fix It