P3400 Code Explained: Cylinder Deactivation System (Bank 1), Often Tied to Oil Pressure

P3400 is a generic OBD-II trouble code that means “Cylinder Deactivation System (Bank 1).” It is not strictly an “oil pressure sensor” code, but it is frequently triggered by low or unstable oil pressure, a clogged oil passage, or a faulty oil pressure switch/solenoid within systems like VCM/AFM/MDS that rely on oil pressure to deactivate cylinders.

What P3400 Means and Why It Appears

P3400 indicates the powertrain control module detected an issue when commanding cylinder deactivation on Bank 1 (the side of the engine containing cylinder 1). Cylinder deactivation systems—Honda/Acura VCM, GM AFM/DOD, Chrysler MDS—use engine oil pressure to collapse lifters or alter rocker actuation and temporarily shut off select cylinders. If the commanded state doesn’t match expected sensor feedback or engine behavior, P3400 sets.

Is P3400 an Oil Pressure Sensor Code?

No. A pure engine oil pressure sensor circuit fault is typically P0520–P0524. However, P3400 commonly involves oil pressure-related components—especially the VCM/AFM/MDS oil pressure switch(s), spool/solenoid assemblies, or restricted oil screens—because oil hydraulics are central to enabling cylinder deactivation.

Common Symptoms

Drivers may notice several operational changes when P3400 is stored. Below is what you’re likely to experience.

• Check Engine Light illuminated; ECO/VCM/AFM/MDS indicator disabled
• Reduced fuel economy (cylinder deactivation not engaging)
• Rough idle or mild hesitation on transition in/out of deactivation
• Possible related codes: P3497 (Bank 2), P0520–P0524 (oil pressure), misfire codes
• In some cases, valvetrain noise if a lifter or deactivation mechanism is sticking

While the vehicle may continue to run, these symptoms signal the deactivation system is offline or struggling, and oil pressure integrity should be checked quickly.

Likely Causes

Multiple issues can lead to P3400, but oil condition and pressure are the most common threads.

• Low engine oil level or degraded/incorrect viscosity oil
• Restricted or dirty oil passages and filter screens in the VCM/AFM/MDS control assembly
• Faulty VCM/AFM/MDS oil pressure switch or sensor
• Defective cylinder deactivation solenoid/spool valve pack or wiring/connector faults
• Sticking/collapsed deactivation lifter(s) or rocker mechanism issues
• Mechanical low oil pressure (worn pump/bearings) or sludge
• Outdated ECM/PCM calibration on some models

Because these systems depend on clean oil at the correct pressure, maintenance history and oil quality are often the quickest clues.

How Technicians Diagnose P3400

A structured diagnostic approach helps isolate whether the fault is hydraulic, electrical, or mechanical.

• Verify code(s) and freeze-frame data; look for companion oil pressure or Bank 2 code (P3497)
• Check oil level, condition, and viscosity; correct immediately if off-spec
• Measure actual oil pressure with a mechanical gauge at hot idle and under load, compare to spec
• Command cylinder deactivation with a scan tool and monitor switch status and RPM response
• Electrically test the deactivation solenoid pack and oil pressure switch (power, ground, continuity)
• Inspect/clean or replace oil control screens/filters at the spool valve or in the valve/valley cover
• If symptoms persist, evaluate for sticking/collapsed lifters and consider borescope/relative compression
• Check for OEM technical service bulletins (TSBs) and PCM/ECM updates

These steps differentiate a simple maintenance fix from a component failure, reducing guesswork and repeat repairs.

Common Fixes

Repairs depend on the root cause discovered during diagnosis.

• Change oil and filter with the OEM-recommended viscosity and quality; clear code and retest
• Replace a failed VCM/AFM/MDS oil pressure switch/sensor
• Service or replace the deactivation solenoid/spool valve assembly; clean or replace its screens
• Repair wiring/connectors to the solenoid pack or pressure switch
• Address mechanical issues: stuck/collapsed lifters, worn oil pump, or sludge remediation
• Apply OEM updates (revised parts/valve covers/deflectors or PCM calibrations) when applicable

In many cases, correcting oil level/viscosity and cleaning screens resolves the fault; persistent codes often point to a sensor/solenoid or lifter issue.

Where You’ll See P3400

The code is most common on engines with factory cylinder deactivation.

• Honda/Acura V6 models with VCM: P3400 = Bank 1; companion code P3497 = Bank 2
• GM (Chevrolet/GMC/Cadillac) V8s with AFM/DOD: Bank 1 deactivation fault
• Chrysler/Dodge/Ram with MDS: Bank 1 deactivation fault

Always confirm the exact code description in your vehicle’s service information, as naming can vary slightly by manufacturer.

Prevention and Best Practices

Preventive maintenance goes a long way toward avoiding P3400 on deactivation-equipped engines.

• Maintain oil at the proper level and change at or before intervals, using OEM-specified viscosity
• Avoid extended oil change intervals if your driving includes short trips or heavy loads
• Address any oil pressure or misfire codes promptly to prevent cascading faults
• Use quality oil filters with proper bypass characteristics
• Keep software up to date when manufacturers issue calibration improvements

Good lubrication practices help keep hydraulic actuators and lifters functioning and reduce the chance of P3400 reoccurring.

Safety and Driveability Notes

With P3400, the vehicle often reverts to full-cylinder operation and remains driveable, but fuel economy may drop. If oil pressure is genuinely low or the engine is noisy, avoid driving and diagnose immediately to prevent engine damage.

Summary

P3400 denotes a Cylinder Deactivation System fault on Bank 1—not a dedicated oil pressure sensor code—but it is closely linked to oil pressure and flow. Start by verifying oil level and quality, then check oil pressure, the deactivation oil pressure switch, solenoids/spool valves, and screens. Address any mechanical lifter or wiring issues, and apply OEM updates where applicable. Timely maintenance and correct oil viscosity are the most effective defenses against P3400.

What is the code for a bad oil pressure sensor?

An oil pressure sensor error code, often indicated by codes like P0520, P0521, P0522, or P0523, signifies a problem with the engine oil pressure sensor or its circuit. These codes suggest the Powertrain Control Module (PCM) is detecting an issue with the oil pressure readings, either due to a faulty sensor, wiring problems, or actual low or high oil pressure. It’s crucial to address these codes promptly as low oil pressure can lead to severe engine damage. 
Understanding the Codes:

• P0520: Indicates a general malfunction in the engine oil pressure sensor or its circuit. 
• P0521: Suggests the oil pressure sensor is reporting readings outside of the expected range or performance parameters. 
• P0522: Indicates a low oil pressure reading from the sensor, potentially due to low oil level, a faulty sensor, or wiring issues. 
• P0523: Indicates a high oil pressure reading from the sensor, which could be caused by a faulty sensor, wiring issues, or mechanical problems with the oil pump. 

Possible Causes:

• Faulty Oil Pressure Sensor: The sensor itself may be malfunctioning and sending incorrect readings. 
• Wiring Problems: Damaged or corroded wiring in the sensor’s circuit can disrupt communication with the PCM. 
• Low Oil Level: Low oil can trigger the sensor to register low pressure. 
• Low Oil Pressure: Problems with the oil pump or oil passages can cause actual low oil pressure. 
• High Oil Pressure: Issues with the oil pump, restricted oil passages, or a faulty sensor can lead to high oil pressure readings. 
• Dirty Oil: Contaminated oil can affect the sensor’s readings. 
• Wrong Engine Oil: Using the incorrect type or viscosity of oil can also affect readings. 
• Faulty Solenoid: In some cases, a faulty solenoid controlling oil pressure can cause error codes. 

Symptoms:

• Check Engine Light illuminated.
• Oil pressure warning light illuminated.
• Oil pressure gauge reading too high or too low.
• Engine starting, stalling, or running poorly.
• Mechanical noises like ticking, knocking, or rumbling.
• Vehicle may enter “limp mode”. 

Recommendations:

• Do not ignore the code: Driving with low oil pressure can cause severe engine damage. 
• Check the oil level and condition: Ensure the oil level is correct and the oil is not dirty. 
• Inspect wiring and connections: Look for any damaged or corroded wires or connections related to the sensor. 
• Consider professional diagnosis: If you are not comfortable with diagnosing the issue yourself, take your vehicle to a qualified mechanic. 
• Replace the sensor if necessary: If the sensor is faulty, it will need to be replaced. 
• Address low or high oil pressure issues: If the code is due to low or high oil pressure, further diagnosis and repair of the oil pump or other related components may be needed. 

What are the symptoms of P3400?

This code is set because of low oil pressure/level, faulty valve timing control solenoid/s, and shorted deactivation circuits. If this code is present, your vehicle can exhibit symptoms like decreased fuel economy, poor engine performance, and logged misfire-related codes.

How do I fix the code P3400?

The P3400 trouble code on your vehicle indicates a problem with the cylinder deactivation system, specifically on bank one, or the valve pause system is stuck off. This can be caused by low oil level or pressure, a faulty oil pressure sensor, or issues with the cylinder deactivation solenoid or its wiring harness. To address this, start by checking the engine oil level and pressure, and ensure the oil is clean. If the problem persists, inspect the oil pressure sensor for damage or clogging, and consider replacing it. You may also need to check and potentially replace the cylinder deactivation solenoid or wiring, or clean the oil passages if they are clogged with debris. 
Here’s a more detailed breakdown of potential causes and fixes:
1. Low Oil Level or Pressure:

• Check the oil level: . Opens in new tabEnsure the oil level is within the recommended range, as indicated in your owner’s manual. 
• Check oil pressure: . Opens in new tabIf the oil level is okay, consider having a manual oil pressure test done to check for low pressure, which can also cause the P3400 code. 
• Oil change: . Opens in new tabIf the oil is old or dirty, consider an oil and filter change, and check the engine passages for sludge or deposits. 

This video explains how to check the oil level and what to do if it’s low: 56sFly BeeYouTube · Mar 4, 2024
2. Oil Pressure Sensor:

• Inspect the sensor: The oil pressure sensor can fail or become clogged with debris, leading to the P3400 code. 
• Replace the sensor: If the sensor is faulty, replacing it can resolve the issue. 
• Check wiring: Inspect the wiring harness and connectors for the oil pressure sensor for damage or corrosion. 

This video demonstrates how to replace the oil pressure sensor: 1mTry This DIYYouTube · Aug 4, 2025
3. Cylinder Deactivation Solenoid:

• Inspect the solenoid: The cylinder deactivation solenoid, also known as the valve pause system solenoid, can fail or become clogged. 
• Replace the solenoid: If the solenoid is faulty, replacing it can resolve the issue. 
• Clean the solenoid: If the solenoid is clogged, cleaning it may be an option. 

This video explains how to check the solenoid and replace it if necessary: 1mAnything AutoYouTube · Dec 9, 2024
4. Wiring Harness and Connectors:

• Inspect the wiring harness: Check for any damage or corrosion in the wiring harness and connectors related to the cylinder deactivation system.
• Repair or replace: Repair any damaged wiring or replace the connector as needed. 

5. Other Potential Causes:

• Lifters: Clogged oil passages or faulty lifters can also cause the P3400 code.
• Engine sludge: In severe cases, a heavily sludged engine may require a complete disassembly for cleaning. 

Important Notes:

• Consult a professional: If you are not comfortable working on your vehicle’s engine, it’s best to consult a qualified mechanic. 
• Clear the code: After making repairs, you may need to clear the P3400 code using an OBD-II scanner. 
• Driving with the code: If the code persists, it’s generally recommended to avoid driving the vehicle, especially in limp mode, as it can damage the engine. 

What does code 3400 mean?

“Code 3400” refers to different things depending on the context, most commonly a diagnostic trouble code (P3400) for a vehicle’s cylinder deactivation system or a workers’ compensation code (3400) for manufacturing metal stamped goods. Other possibilities include sections of the California Code of Regulations (e.g., Title 8, Section 3400 for medical services) or the California Probate Code (Section 3400) related to a minor’s total estate. 
Here are the most common meanings for “Code 3400”:
For Automobiles (P3400):

• Meaning: This is a diagnostic trouble code (DTC) that indicates a problem with the Cylinder Deactivation System on Bank 1. This system saves fuel by shutting down certain cylinders, but the code means a cylinder failed to deactivate as commanded by the engine’s computer. 
• Symptoms: A “Check Engine” light, decreased fuel efficiency, loss of engine power, or generally poor engine performance. 
• Common Causes: Low engine oil level or pressure, a faulty cylinder deactivation solenoid, or issues with the solenoid’s wiring or other related sensors. 

For Workers’ Compensation (Class Code 3400): 

• Meaning: This is a workers’ compensation classification for businesses that manufacture metal stamped goods.
• Activities: The code applies to operations involving extensive stamping, punching, blanking, or shearing of sheet metal.
• Examples of Products: Metal brackets, electrical fittings, lamp parts, and unfinished trays.

Other Meanings (Legal/Government Codes):

• California OSHA (Title 8, Section 3400): . Opens in new tabThis section of the California Code of Regulations deals with medical services and first aid, requiring employers to provide adequate first-aid materials and emergency eyewash/body flush facilities in case of corrosive material exposure. 
• California Probate Code, Section 3400: . Opens in new tabThis section defines “total estate of the minor” for the purpose of administering a minor’s assets and lists what can be deducted when computing that total estate. 
• California Public Contract Code, PCC § 3400: . Opens in new tabThis code addresses the timing of data submissions after a public contract is awarded and provides exceptions, such as when a specific brand or trade name product is necessary. 
• California Family Code, FAM § 3400: . Opens in new tabAlso known as the Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA), this code establishes rules for determining which state’s courts have jurisdiction over child custody matters.