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P3400 Code: Causes, Symptoms, and How to Fix It! 

  • Cars Explained
  • Gerard Stevens
  • 7 minutes

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How will you feel when you observe a sudden decrease in your car’s engine performance while driving? You know there’s something wrong with your engine but will be confused about the actual reason. The check engine will be on too. You need to use an OBD II scanner to identify the exact issue with the engine. On checking, it may show the P3400 code! 


When the check engine light comes on for the P3400 code, it can denote the ‘Service Engine Soon warning light or the ‘Engine Light ON.’ However, be aware that car manufacturers have a different definition for this Diagnostic Trouble Code (DTC). This code can appear for various reasons, and a mechanic will need to figure out what caused it in your case. 

So, what are the causes and symptoms of the P3400 code? How can you fix it? Continue reading to know more! 

What does the P3400 code mean? 

Engine error code P3400  means ‘Cylinder deactivation system – Bank 1’. The code activates when the Powertrain Control Module (PCM) recognizes a fault, failure, or malfunction in any part or component of the cylinder deactivation system that prevents it from working properly. Be mindful that the code can also activate when any part or component in the cylinder deactivation system fails or malfunctions, allowing it to work when it shouldn’t.  

A cylinder deactivation system is a mechanism that allows an engine to run on fewer cylinders than standard engines. When an engine runs on partial cylinders, it consumes less fuel while producing the same power as a regular engine. On V-type engines, ‘Bank 1’ refers to the cylinder bank that contains cylinder 1. Automobiles commonly experience this fault are Honda, Dodge, Chevrolet, Pontiac, GMC, and Chrysler. 

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What causes code P3400? 

The most common causes of the P3400 code are quite the same across all cars and include one or more of the following.  

  • Faulty cylinder deactivation solenoid 
  • Oil level gets low 
  • Contaminated, degraded, or unsuitable engine oil 
  • Faulty, burnt, shorted, corroded, or disconnected wiring or electrical connectors 
  • Malfunctioning or unsuitable Mass Airflow Sensor or Intake Air Temperature Sensor 
  • Faulty or unsuitable Throttle Position Sensor 
  • The lifters have poor oil pressure 
  • Faulty lifters 
  • An open or short circuit in the cylinder deactivation solenoid connection 
  • A faulty electrical connection in the cylinder deactivation solenoid circuit 
  • A malfunctioning VVT (Variable Valve Timing)oil control solenoid 
  • Failure of the PCM or another control module. Though it is an uncommon occurrence, it requires looking for the fault elsewhere before replacing any control module. 

What are the symptoms of the P3400 code? 

Typical code P3400 symptoms are almost the same across all cars and may include one or more of the following. But the intensity of one or more symptoms may differ between the cars. 

  • Check engine light turns on 
  • Engine starts vibrating 
  • Engine performance goes down 
  • A sharp increase in fuel consumption  
  • The engine may run rough or stall regularly and suddenly 
  • The PCM may initiate a fail-safe or limp mode in some instances, which will last until the fault gets rectified 


How serious is the P3400 code? 

Usually, the P3400 code doesn’t cause a serious threat to your car. However, the following can happen to your when the code activates. 

  • The car will run on all eight cylinders rather than four when this code activates. 
  • The code results in a decrease in fuel economy and an increase in engine emissions. 
  • Although the P3400 DTC is not threatening to your car, it is crucial to have it diagnosed as soon as possible. 

Is it safe to drive with a P3400 code? 

Although a P3400 problem is unlikely to cause immediate engine damage, you should have it checked at the earliest. Your car will run on all eight cylinders as long as the code is active, resulting in reduced fuel economy and greater emissions. 

What happens if you ignore engine code P3400? 

There is a comparatively minor risk involved if the cylinder deactivation system fails. The most common issue will be that your car starts experiencing fuel efficiency. However, the most typical reasons for this system failure can result in severe engine issues. Your car’s engine could fail if you don’t diagnose it on time. In addition, it can injure you or cost a lot of money to repair. 

How to diagnose P3400 code 

These are the steps that a mechanic follows while diagnosing the code. 

Steps to follow 

  • Check oil levels and engine oil pressure. 
  • Use an OBD-II scanner to collect all DTCs stored in PCM.  
  • If the PCM has stored deactivation and/or oil pressure DTCs, diagnose them first. 
  • Clear trouble codes with an OBD-II scanner. 
  • Then inspect the cylinder deactivation solenoid #1 by triggering it with a scan tool. The solenoid will vibrate and make a clicking noise if working properly. Clear the oil passageways and replace the solenoid if it isn’t working. 
  • If solenoid #1 is working properly, then inspect the cylinder deactivation solenoid #7. 
  • Then test the solenoid #7. The solenoid will vibrate and make a clicking noise if working. If not working, clear the oil passageways and replace the solenoid.  
  • If solenoid #7 works, check the oil passages to the lifter. 
  • Clear oil channels if needed. The mechanic may need to disassemble the engine block. 
  • Replace the lifters if oil passageways have blockages.   

Common mistakes that happen while diagnosing the code 

One common mistake when diagnosing this code is ignoring to check the oil passageways for dirt and mud. Blocked oil passageways will reduce engine oil pressure and stop the cylinder’s deactivation solenoids and lifters from functioning properly when switching from V4 to V8 mode. Therefore, the mechanics should always check the oil passageways thoroughly so that you don’t have to spend dollars on unnecessary parts and repairs. 

How do I fix code P3400? 

It’s almost impossible to fix this DTC by yourself. Instead, you will have to get the help of a skilled mechanic to reach the affected engine parts. A skilled mechanic will inspect various engine components and test certain cylinders to determine if they are working properly during this service. 

What repairs can fix the P3400 code? 

car engine repair

The real cause of the problem determines the extent of your car’s repair. Here are a few things mechanics can do to get rid of the P3400 error code. 

  • Replacement of cylinder deactivation solenoid #1 
  • Replacement of cylinder deactivation solenoid #7 
  • Remove dirt and debris from cylinder deactivation solenoid oil passageways  
  • Make lifter oil passageways free from dirt and debris 
  • Replacement of engine lifters 
  • If dirt and mud cover the entire engine, it will be necessary to disassemble the entire engine to clean it properly 

How much does it cost to fix the P3400 code? 

Typically, repairing a P3400 error code costs you anything between $75 and $150 an hour. The real cause of the issue and the technician’s skill determines the expected repair time. 

The bottom line 

  • The P3400 code indicates that P3400 there is a performance problem with the Cylinder Deactivation System in Bank 1. 
  • The engine performance decreases, and fuel consumption increases when your car encounter this code. 
  • Usually, the code doesn’t cause sudden damage to your car. However, the engine will start failing if you don’t diagnose the code for a long period. 
  • It is difficult to fix the issue by yourself. So, always get the help of a skilled technician to rectify this engine error code. 
  • The time needed to fix the issue depends on the real cause and the technician’s skill. Normally, it will cost you anything between $75-$150 for the repair. 

Save well when you fix car engine code P3400

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