Honda OBD-II Code P3400: Cylinder Deactivation (VCM) System Fault on Bank 1

P3400 on a Honda engine indicates a fault in the Cylinder Deactivation System—Honda calls it Variable Cylinder Management (VCM)—on Bank 1 (the cylinder bank that includes cylinder 1). In most cases, the engine computer detected that the oil-pressure-based control for deactivating cylinders on Bank 1 did not behave as expected, often due to low/incorrect oil, a failing rocker arm oil pressure switch, a clogged oil control/solenoid screen, or wiring issues. The vehicle typically disables VCM, turns on the check-engine light, and continues running on all cylinders.

What the code means and why it appears

P3400 is set when the powertrain control module (PCM) commands cylinder deactivation on Bank 1 but doesn’t see the correct confirmation from the rocker arm oil pressure switch or related sensors. Honda’s V6 engines use oil pressure to lock/unlock special rocker arms that enable cylinder shutoff at light loads for better fuel economy. If oil pressure, switch feedback, or solenoid control isn’t right, the PCM logs P3400 and suspends VCM to protect the engine.

Typical symptoms you may notice

Most drivers experience minor drivability changes with the malfunction indicator lamp (MIL) illuminated. The system usually reverts to full-cylinder operation.

Below is a list of common symptoms owners report when code P3400 is present.

• Check-engine light on; ECO light may stop appearing during cruise
• Reduced fuel economy (VCM disabled)
• Occasional shudder or roughness during light-throttle transitions
• No-start or severe drivability issues are uncommon

While symptoms are often mild, the warning light indicates a system fault that should be diagnosed to prevent longer-term issues or repeated MIL illumination.

Common causes on Honda/Acura V6 engines

Because VCM depends on clean oil and precise hydraulic control, anything that disrupts oil pressure or signal feedback can trigger P3400.

• Incorrect, low, or degraded engine oil (wrong viscosity or overdue change)
• Faulty Bank 1 rocker arm oil pressure switch (sensor) or intermittent connector
• Clogged oil control (VCM/VTEC) spool valve screen or sticky spool valve
• Wiring/connector damage in the Bank 1 harness near the rear cylinder head/firewall
• Low engine oil pressure due to internal wear or a weak oil pump (less common)
• PCM software sensitivity (some models benefit from software updates)

On transverse V6 Hondas, Bank 1 is typically the rear cylinder bank (closest to the firewall). Heat and limited access can accelerate sensor or wiring issues in this area.

How technicians diagnose P3400

A systematic approach prevents unnecessary parts replacement. The following steps outline a proven workflow used by technicians.

1. Verify the code and note freeze-frame data (speed/load/temp when it set; often during steady highway cruise).
2. Check engine oil level, condition, and viscosity; correct to the spec on the oil cap/owner’s manual (0W-20 or 5W-20 depending on model/year).
3. Inspect Bank 1 wiring/connectors at the rocker arm oil pressure switch and VCM/VTEC solenoid assembly for oil intrusion, corrosion, or damage.
4. Command the VCM/solenoid on/off with a scan tool (if supported) and monitor the switch signal; verify that the switch changes state as expected.
5. Measure reference voltage and continuity for the switch circuit per service manual pinouts.
6. Inspect/clean or replace the spool valve gasket and its fine mesh screens if debris is present.
7. Check mechanical oil pressure with a gauge if electrical tests pass or oil-related issues are suspected.
8. Review TSBs/updates; reflash PCM if an update addresses false triggers for P3400/P3497.

Completing these steps usually isolates whether the fault is fluid/maintenance-related, electrical (switch/wiring), or mechanical (oil pressure/valve actuation).

Likely fixes and typical costs

Repairs depend on findings. The items below reflect common resolutions for P3400 on Honda/Acura V6s.

• Engine oil and filter service with correct viscosity: low cost; often resolves marginal cases
• Replace Bank 1 rocker arm oil pressure switch: moderate cost; a frequent failure point
• Replace/clean VCM/VTEC spool valve gasket and screens; in some cases, the solenoid assembly: moderate cost
• Repair wiring/connectors at rear cylinder head: variable cost depending on damage
• PCM software update (dealer or qualified shop): moderate cost; addresses sensitivity/logic on some models
• Address low base oil pressure (oil pump/internal wear): higher cost; least common

Many P3400 cases are resolved without major engine work. Starting with oil service and sensor/screen evaluation is often the most cost-effective route.

Is it safe to keep driving?

In most cases, yes—P3400 forces the engine to run on all cylinders, so drivability remains largely normal, but fuel economy can drop. Avoid heavy loads or extended high-speed driving until you’ve confirmed proper oil level/condition. Prolonged driving with contaminated or low oil can lead to accelerated engine wear.

Models and engines commonly affected

P3400 appears most often on Honda/Acura V6 models equipped with VCM, especially in certain years of the J-series engine family.

• Honda Accord V6, Odyssey, Pilot, and Ridgeline (various model years with VCM)
• Acura MDX, RDX V6, TL/TLX V6 where equipped with cylinder deactivation

Coverage varies by market and year; consult your VIN-specific service information to confirm component locations and procedures.

Related codes and how they differ

Understanding companion codes can speed diagnosis.

• P3497: Cylinder Deactivation System, Bank 2 (front bank on most transverse V6 Hondas)
• Oil-pressure or VTEC-related codes (e.g., P2647/P2646) can point to shared oil control issues

If P3400 and P3497 appear together, start with oil quality/pressure and spool valve screens, then test both banks’ switches and wiring.

Prevention tips

Good maintenance is the best defense against VCM faults.

• Use the exact oil grade specified for your model year and climate
• Change oil and filter on time; severe-service intervals may apply
• Address any oil leaks promptly to prevent low level
• Keep connectors clean and secured, especially near the rear cylinder head
• Ask your dealer about applicable PCM updates if you’ve had repeated VCM-related codes

Following these practices reduces the chance of oil-pressure and control issues that trigger P3400.

Bottom line

P3400 on a Honda indicates a Bank 1 cylinder deactivation (VCM) malfunction, most commonly tied to oil condition/viscosity, a failing rocker arm oil pressure switch, or clogged oil control screens. Verify oil first, then test the Bank 1 switch, solenoid, and wiring; consider PCM updates where applicable. The vehicle usually remains drivable, but prompt diagnosis prevents repeat faults and maintains efficiency.

What does valve pause system mean?

The Valve Pause System (VPS) is part of Honda’s powertrain control system. Prior to replacing any components the technician will verify the engine oil level is full and of good quality. This system uses oil pressure as high as 35 to 50 PSI to activate the Valve Pause System (VPS).

What is the code P3400 cylinder deactivation system bank 1?

The powertrain control module (PCM) will register a P3400 trouble code when the cylinder fails to deactivate upon the computer’s command. This code is set because of low oil pressure/level, faulty valve timing control solenoid/s, and shorted deactivation circuits.

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 8, 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.