What Does the Engine Code P3400 Mean?

Engine code P3400 indicates performance issues with your car’s bank one cylinder deactivation system.
Written by Max Werner
Reviewed by Melanie Reiff
A P3400 code occurs during a performance issue with your vehicle's cylinder deactivation system, which is used to change between V8 and V4 modes. 
When the code is displayed, your vehicle will only operate in V8 mode—forcing your car to consume additional fuel and thus increasing engine emissions.
Modern vehicles rely on diagnostic trouble codes (DTCs) to alert drivers to engine issues. While OBD-II code readers can explain what these codes mean, they cannot identify the cause of the issue. Diagnosing severe codes will require the help of a skilled auto technician.
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What does the engine code P3400 mean?

Definition: Cylinder deactivation system performance issue detected
V8 engines operate by switching between two different modes. When starting, idling, or experiencing heavy loads, your vehicle uses all eight cylinders. Less strenuous conditions will only require four cylinders.
A control system collects values from the MAF, MAP, and TP sensor to determine the right time to switch modes. When problems with the deactivation system arise, you’ll see the P3400 code—and your vehicle will be locked into 8-cylinder functioning.

How much will it cost to fix?

Repairing a P3400 code will cost between $75 and $150 per hour. The estimated repair time will depend on technician skill and what caused the alert.

What can cause the P3400 engine code?

Failure in multiple systems can cause a P3400 engine code, but the most common issues are as follows:
  • Faulty cylindrical deactivation solenoid
  • Cylinder deactivation solenoid harness is open or shorted
  • Poor electrical connection in cylinder deactivation circuit
  • Defective mass airflow sensor
  • Low engine oil
  • Poor oil pressure on the filters

Common symptoms of the P3400 engine code

check engine light
will be the first symptom that you have a P3400 code. You may also notice that your engine vibrates when idle.

How serious is the P3400 engine code? 

A P3400 issue doesn’t risk immediate damage to your engine, but you should have it checked out as soon as possible
As long as the code is active, your vehicle will only function using all eight cylinders, the effects of which are a worse fuel economy and increased emissions.

Can I fix the P3400 engine code myself?

You likely won’t be able to fix this code on your own, as even reaching the affected engine components requires a skilled mechanic. 
During this service, an auto professional will inspect various elements of your engine and test certain cylinders to see if they are working correctly.

What repairs can fix a P3400

The level of repair your vehicle needs greatly depends on the cause of the issue. Here are some fixes mechanics might make to get rid of the P3400 code:
  • Replace one of the cylinder deactivation solenoids
  • Clean dirt or debris from oil passages
  • Replace lifters in the engine
In severe cases, a mechanic may need to disassemble the engine entirely to clean each component thoroughly.

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