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P3400 Code – What Does It Mean & 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.


The Cylinder Deactivation System Bank 1 (P3400) is an error code that can appear on some cars. It means the car’s ECU has detected a problem with the bank 1 cylinder deactivation system. 


A cylinder deactivation system is the device that allows an engine to run on a fewer number of cylinders than traditional engines. When an engine is running on partial cylinders, it can consume less fuel while still maintaining the same power of a traditional engine.


There can be several causes that can trigger the P3400 error code. First and foremost it can simply be that the cylinder deactivation solenoid is worn out or defective. The solenoid wiring could be shorting out. 

Malfunctioning lifters and blocked oil passages are a common cause for the P3400 code, along with having a low engine oil level.


  • The “check engine” light is displayed on your instrument panel.
  • Engine vibration –  the engine may feel like it’s running rough or miss when it’s idling.


Note: If you do not or cannot perform the following steps then please get with a certified automobile technician. They have the skills and the knowledge to properly diagnose the P3400 code.

Check to make sure your engine oil is at a proper level. Make sure the engine pressure is reading normally.

Be sure you have an OBDII scanner handy and plugged into your vehicle’s diagnostic port. The scanner will be able to verify the proper error code. You’ll be able to record and clear the codes also.

You can pick up a scanner at nearly any automotive store, or just take your vehicle to a certified mechanic.

The auto technician will be testing the cylinder deactivation solenoid first. This will be done by actuating the number 1 solenoid with the scanner. 

If the solenoid works, you’ll hear an audible click and see the solenoid vibrate a bit. 

If it’s not working, there’s a few things that can be checked:

  • Inspect the oil passages for packed mud and other debris
  • If the passages are blocked, clean them out
  • You may have a defective solenoid. Replace it if needed

The next step is to test the cylinder deactivation solenoid-7. 

  • Just repeat the steps from above. If the solenoid is found to be defective, go ahead and replace it. 

Once cylinder deactivation solenoid-7 has been verified as functional or not, the next step is to inspect the engine’s oil passages. Why is this? Over time the passages can collect dirt, mud and grime.

So go ahead and inspect and clean out any restricted oil passages that need it. If the oil passages are clean, the problem will be that the lifters will need replacement.

Common mistakes

One thing that gets missed when troubleshooting P3400 is that it’s very easy to forget about inspecting the oil passageways. When they get gummed up with dirt, mud and sludge there will result in reduced engine oil pressure. 

In turn, the cylinder deactivation solenoids and lifters won’t be able to switch from 4 cylinder to V8 cylinder mode properly.

How serious is this?

The P3400 code is not normally a totally serious condition. Your vehicle will keep operating with 8 cylinders instead of 4. 

You can expect things such as an increase in engine emissions, and absolutely terrible fuel economy. Naturally, you don’t want the problem to go for a long period of time before getting to the root of the problem.

What repairs can fix the code?

  • Please do not let your engine oil get so dirty that you’ll need to get the oil passages cleaned out. Perform your oil changes at the recommended schedule. It would be a costly mistake if your oil passages get clogged.
  • Replace cylinder deactivation solenoid #1 if necessary
  • Also, replace cylinder deactivation solenoid #7 if it’s not functioning properly
  • If the problem isn’t the oil passages, you’ll probably end up replacing the your engine’s lifters

Related codes

  • P3401 – Cylinder 1 Solenoid
  • P3409 – Cylinder 2 Solenoid
  • P3417 – Cylinder 3 Solenoid
  • P3425 – Cylinder 4 Solenoid


We hope you were able to get some much needed information from this article. We’ve discussed the P3400 OBDII error code, its definition, meaning and causes for the error. We also went over how to diagnose the error code and showed you how to repair potential problems. 

Never let any type of OBDII problems persist in your vehicle, as it might cost you big time in the end. 

P3400 Code – What Does It Mean & How To Fix It