P3400 – Cylinder Deactivation System


By Reinier (Contact Me)
Last Updated 2020-08-10
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P3400 Cylinder Deactivation System

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What Does Code P3400 Mean?

OBD II fault code P3400 is a generic trouble code that is defined as “Cylinder deactivation system – Bank 1”, and is set when the PCM (Powertrain Control Module) detects a fault, failure, or malfunction in any part or component in the cylinder deactivation system that prevents the system from functioning, and/or functioning correctly. Note that code P3400 will also set when a fault, failure, or malfunction in any part or component in the cylinder deactivation system occurs that allows the system to operate when it should not. Note that “Bank 1” refers to the bank of cylinders on V-type engines that contains cylinder #1.

The purpose of cylinder deactivation systems, also known as variable displacement systems, is to deactivate some cylinders in an engine under some operating conditions to save fuel, and to reduce emissions. In practice, these systems will only become operational when not all of an engines’ power is required, such as during light engine loads or steady highway cruising speeds.

In terms of operating principles, the PCM will continuously collect data from a variety of engine and other sensors, including the Mass Airflow Sensor, Throttle Position Sensor, Intake Air- and Coolant Temperature Sensors, Engine Speed Sensor, and others to calculate the total load on the engine at any given point in time. When the PCM deems conditions suitable for cylinder deactivation, it will energize oil control solenoids that allow pressurized engine oil to act on both the intake and exhaust valves of affected cylinders.

This action not only closes all the valves on the deactivated cylinders but it also disables both the ignition system and fuel injectors on the affected cylinders, which on engines with 8 and more cylinders, can be as high as 50% of all cylinders on the engine. The action of closing valves and keeping them closed traps the exhaust gasses from the last power stroke in the cylinder to act as “springs” that both compress and expand under the piston’s movement, which helps to maintain engine balance.

When operating conditions change and full engine power is required, such as during overtaking slower traffic, the valves on the deactivated cylinders are reactivated, and both ignition and fuel delivery is restored. While this switching is sometimes noticeable in engines with 4 or 6 cylinders, the process is largely seamless and undetectable in vehicles that have engines with 8 and more cylinders.

Regardless of the number of cylinders on any given engine though, cylinder deactivation systems are intended to be operational only under very clearly defined operating conditions. Therefore, if the PCM detects faults, failures, or malfunctions in any associated sensor and/or electrical circuit that affect either the activation or deactivation of the system, it will set code P3400, and illuminate a warning light. Note that on some vehicles, the PCM will only set a code and illuminate a warning light on the second consecutive failure of the cylinder deactivation system.

Where is the P3400 sensor located?


Even though most cylinder deactivation systems use many, if not most of the components that control variable valve timing systems, there are too many different designs in use today to indicate the location even a small fraction of all relevant components here.

Instead, this image shows a typical deactivation pattern on V8 engines, with the pistons in red remaining active, while the blue pistons are those that have been deactivated. Note that while some designs disable cylinders in opposite pairs, other designs disable cylinders in equal numbers on each bank, with the firing order determining which cylinders are disabled on which bank of cylinders. Nonetheless, all designs will deactivate cylinders in such a way that engine balance is not compromised.

What are the common causes of code P3400?

The typical causes of code P3400 are largely similar across all designs and applications and could include one or more of the following-

  • Low oil level
  • Dirty, degraded, contaminated, or unsuitable engine oil
  • Insufficient oil pressure
  • Burnt, damaged, shorted, corroded, or disconnected wiring and/or electrical connectors
  • Defective, malfunctioning, or unsuitable Mass Airflow Sensor
  • Defective, malfunctioning, or unsuitable Intake Air Temperature sensor
  • Defective or malfunctioning Throttle Position Sensor
  • Defective or malfunctioning VVT (Variable Valve Timing)oil control solenoid- note that in many designs, the VVT solenoid also serves to activate and deactivate the cylinder deactivation system
  • Failed or failing PCM or another control module, which is a rare event so the fault must be sought elsewhere before any control module is replaced

What are the symptoms of code P3400?

Typical symptoms of code P3400 are much the same across all designs and applications, and could include one or more of the following, but note that the severity of one or more symptoms could vary between designs and applications-

NOTE: Cylinder deactivation systems typically require that all implicated sensors operate within narrowly defined ranges or voltages before the system can be activated. Therefore, any implicated sensor that is not operating correctly can prevent the cylinder deactivation system from working, or if it has been operational, from deactivating. As a result, code P3400 can sometimes be accompanied by multiple other codes that, at first sight, might not appear to be related to P3400.

  • Stored trouble code and illumined MIL (CHECK ENGINE) light
  • Note that multiple codes relating to both misfires and cylinder power contributions could be present along with P3400
  • Reduced engine performance
  • Fuel consumption may increase sharply
  • Engine may run roughly or may stall unexpectedly and repeatedly
  • In some cases, the PCM could initiate a fail-safe or limp mode that will persist until the fault is corrected

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